Amman, Jordan (CNN) Was an American hostage held in Syria killed by a Jordanian airstrike? That's what ISIS said in an online posting Friday, claiming that she died in the group's de facto capital, Raqqa. 
 
 The posting Friday included a picture of a collapsed building and a claim that the woman -- confirmed by her family to be Kayla Mueller -- was being held there. 
 
 But it did not show a body or provide any proof of death. 
 
 Jordanian government spokesman Mohammed al-Momani said his country is looking into the claim. But, he said, "we are highly skeptical" because of ISIS's proven lack of credibility, and he questioned whether they could identify Jordanian warplanes so high in the sky or would hold a hostage in a "weapon warehouse." 
 
 Later, he told CNN that ISIS uses "these events to manipulate facts and to manipulate public opinion." 
 
 "What we know about this terrorist organization is that they are liars when it comes to these things," al-Momani told "The Situation Room with Wolf Blitzer." 
 
 Interior Minister Hussein Majali also knocked down the report, calling it another "PR stunt" by ISIS. 
 
 "They tried to cause problems internally in Jordan and haven't succeeded," Majali said. "They are now trying to drive a wedge between the coalition with this latest low PR stunt." 
 
 ISIS has held a number of hostages from the United States, Britain and Japan. As of now, at least two Westerners are thought to be in its custody: British journalist John Cantlie, who has appeared in a number of ISIS-produced videos, and the American woman, who is a 26-year-old aid worker. 
 
 CNN has not previously named Mueller because of a request from the family. 
 
 Friday night, her parents, Carl and Marsha Mueller of Prescott, Arizona, issued a statement asking the people holding their daughter to contact them. 
 
 "After going to extraordinary efforts to keep Kayla's name out of the media for so long, by securing the cooperation of journalists throughout the world, her name was released today. This news leaves us concerned, yet, we are still hopeful that Kayla is alive. We have sent you a private message and ask that you respond to us privately." 
 
 Asked about ISIS's claim of the woman's death in Raqqa, State Department spokeswoman Marie Harf said that she could not "confirm those reports in any way." 
 
 "Obviously (we are) deeply concerned...," she added. "We have not, at this point, seen anything that corroborates (ISIS's) claims." 
 
 The Prescott, Arizona, native was taken captive in August 2013 in Aleppo, Syria, after leaving a Doctors Without Borders hospital, her family said. 
 
 Before that, Mueller graduated from Northern Arizona University and spent years traversing the world -- including India, Israel and her native Arizona, where she worked in an HIV/AIDS clinic and volunteered at a women's shelter. Her going to Syria in late 2012 with the Danish Refugee Council and Support to Life humanitarian agency aligned with that same mission to help others. 
 
 What drove her? According to her family, Mueller would say, "I find God in the suffering eyes reflected in mine. If this is how you are revealed to me, this is how you are revealed to me, this is how I will forever seek you." 
 
 According to a source close to the family, ISIS had set a deadline of August 13, 2014, for a 5 million Euro ransom to be paid or the group would kill her. 
 
 Experts: Claim is dubious, but possible 
 
 When it comes to ISIS, there's plenty of reason for skepticism. 
 
 Most of its hostages have been executed by the terror group, which then touted the grisly deaths online. 
 
 That was the case with Jordanian pilot Lt. Moath al-Kasasbeh, who was captured by the Islamist extremist group after his F-16 fighter jet crashed while on an anti-ISIS mission near Raqqa. Video emerged Tuesday of ISIS burning him alive while he was locked in a cage. 
 
 After the video came out, Jordanian officials said they have reason to believe al-Kasasbeh was actually killed in early January. That suggested that during the month between, while signaling its openness to a prisoner exchange with Jordan, ISIS had known all along that the pilot was dead. 
 
 CNN terrorism analyst Paul Cruickshank is among those very dubious that ISIS is telling the truth this time around, including its claim that the U.S. hostage was alone in the building and that no militants died in the strike. 
 
 "It seems very, very convenient for propaganda purposes, from the ISIS point of view," Cruickshank said. 
 
 CNN law enforcement analyst Tom Fuentes also cast doubt. The buildings in the photo are damaged but there is no smoke. If the pictures were taken just after an airstrike, there would be smoke from smoldering debris, he said. 
 
 Retired U.S. Army Lt. Col. James Reese, a CNN global affairs analyst, says it's plausible a hostage may have been inadvertently killed in Syria. 
 
 "We all know that (the U.S.-led military coalition's) intelligence ... in Syria is not as good as we have in Iraq now," Reese said. "So it is plausible (Mueller was killed), and it could be unfortunate. But sometimes ... that happens in these wars." 
 
 Though there is no evidence Mueller was killed, U.S. intelligence and law enforcement agencies are working on a theory that she may have died weeks or months ago, sources said. 
 
 Intelligence and law enforcement sources said the theory comes from prior intelligence on her captivity and ISIS' past behavior with hostages. 
 
 The claim of the Jordanian airstrike killing her likely is a convenient way for ISIS to explain why it killed a woman, which could be problematic for its message, the sources said. 
 
 Jordanian airstrikes follow pilot's death 
 
 This all comes in the wake of al-Kasasbeh's horrific killing, which spurred outrage in Jordan and beyond. 
 
 His father, Safi al-Kasasbeh, afterward called on Jordan and its allies to "annihilate" ISIS. Government officials appear, at least in their rhetoric, determined to do just that. 
 
 JUST WATCHED What are Jordan's military capabilities? Replay More Videos ... MUST WATCH What are Jordan's military capabilities? 01:02 
 
 "(Jordan will extract) revenge that equals the tragedy that has befallen the Jordanians," government spokesman Mohammad al-Momani said. 
 
 On Thursday -- a day after executing two jihadists in retaliation -- the Middle Eastern nation launched its first strikes since the news emerged about al-Kasasbeh. 
 
 A squadron of warplanes from the Royal Jordanian Air Force on Friday carried out a number of strikes against ISIS targets, the military said in statement. The Jordanian armed forces did not immediately provide details on the number of aircraft nor what targets were hit. Activists told CNN that one strike killed 47 ISIS fighters. 
 
 Jordanian minister: 'This is definitely our war' 
 
 Until now, ISIS hasn't shown any inclination to back down. Just the opposite, in fact: The terror group has been relentless and brutal in its quest to establish a vast caliphate under its strict, twisted version of Sharia law. 
 
 The organization's savagery seemingly knows no bounds, not only in its use of captives' killings as grisly propaganda tools but in its campaign of mass killings, rapes, kidnappings and other atrocities while taking over swaths of Iraq and Syria. 
 
 Just this week, a U.N. report claimed ISIS has stepped up its use of children in its bloody campaign, even putting price tags on some and selling them as slaves. 
 
 JUST WATCHED Pilot's uncle: Whatever it takes to destroy ISIS Replay More Videos ... MUST WATCH Pilot's uncle: Whatever it takes to destroy ISIS 03:28 
 
 Al-Kasasbeh's killing was an attempt by ISIS "to instill terror and fear in the hearts of its enemies," making them less willing to provoke or put up a fight, says a prominent Sunni Muslim cleric who has been exiled from Syria. 
 
 "What's happening is the opposite," Shaykh Muhammad al-Yaqoubi told CNN's Christiane Amanpour this week. "The martyrdom of Moath has united Muslims ... against ISIS, leaving no slight room of doubt that these people do not represent Islam. They represent savagery, terrorism and extremism." 
 
 That seems to be the sentiment in Jordan, at least, where citizens rallied again Friday in Amman to honor al-Kasasbeh and condemn his killers. 
 
 Thousands filled the King Hussein Mosque there, listening to a sermon decrying ISIS as antithetical to Islam and insisting that Muslims cannot stand idly by. 
 
 After prayers, crowds spilled out onto the streets to march calmly and defiantly toward Palm Square. Many held up banners and signs -- including Queen Rania, with a poster that read, "Moath, the martyr of justice" -- and chanted, "Long live the King." 
 
 JUST WATCHED Jordan foreign minister: Beginning of 'retaliation' Replay More Videos ... MUST WATCH Jordan foreign minister: Beginning of 'retaliation' 03:43 
 
 Jordan for months has been one of a handful of nations in the region taking part in the U.S.-led coalition, a fight it continued with airstrikes Thursday and Friday at different sites around Iraq and Syria. 
 
 For all the efforts of the United States and its allies, Majali, the interior minister, told CNN that the fight is personal for his fellow Jordanians. And King Abdullah II has given "carte blanche ... to the armed forces" to carry it out, Majali said. 
 
 "This is definitely not the U.S.'s war. This is definitely our war," said Majali. "... I don't want to equate ourselves with this evil force (ISIS), but we will (take) revenge for our pilot." ||||| The parents of an American woman held hostage by ISIS revealed they had privately communicated with the terror group before it claimed she was killed a recent Jordanian airstrike. 
 
 A statement that circulated Twitter on Friday said an airstrike outside Raqqa, Syria, killed Kayla Mueller. The statement used her full name, which had not been public. 
 
 The claim could not be immediately confirmed and ISIS did not provide photographic evidence of Mueller’s death, as the group has in the past with other hostages and its own fighters. 
 
 Courtesy Mueller Family 
 
 In a statement released Friday night, Mueller's parents said, "This leaves us concerned, yet, we are still hopeful that Kayla is alive." 
 
 Addressing Kayla's captors directly, Carl and Marsha Mueller also requested that the terror group respond to their private communications. 
 
 "Kayla's mother and I have been doing everything we can to get her released safely. At this time we ask you, who are holding Kayla, to contact us privately," the statement said. 
 
 A spokesperson for the White House National Security Council said they have “not at this time seen any evidence that corroborates ISIL’s claim,” using an alternate acronym for the terror group. 
 
 A Jordanian official told ABC News ISIS's claim was "illogical" and was part of the terror group's public relations campaign. "We need to be very careful not to fall in their trap," the official said. 
 
 Jordan's Foreign Minister Nasser Judeh, called ISIS's claim "an old and sick trick." 
 
 "So they behead innocent #US #UK & Japan hostages & BURN a brave #jordan pilot ALIVE & now a hostage is killed by an airstrike? Sure! Sick!" Judeh said on Twitter, referring to previous atrocities apparently committed on camera by ISIS fighters. 
 
 The ISIS statement appeared to contain some discrepancies, including Thursday’s date on accompanying pictures purportedly showing the building that was struck, while the statement claimed the strikes occurred during Friday prayers. ISIS also claimed Mueller, 26, was the only person killed in that particular airstrike, with none of its fighters injured or killed. 
 
 The Daily Courier 
 
 Officials believe ISIS has misled the public before about the fate of hostages. The Jordanian government said ISIS killed a Jordanian pilot the terror group was holding a month ago, even though the terror group pretended he was alive during hostages negotiations last week. 
 
 In August, ABC News reported ISIS had demanded $6.6 million for Mueller's release. 
 
 “We are pouring through information right now,” one U.S. official said, “but there is no hard evidence” that Mueller has been killed. Another official said that U.S. intelligence had reason to believe Mueller was alive as of a few weeks ago. 
 
 Mueller, from Prescott, Ariz., was kidnapped Aug. 4, 2013 after leaving a Spanish Doctors Without Borders hospital in Aleppo, Syria, according to information provided by a family spokesperson. 
 
 She had graduated from Northern Arizona University in 2009 and “has devoted her career to helping those in need in countries around the world,” the family spokesperson said. 
 
 "Kayla has devoted her life to serving others," Arizona Governor Doug Ducey's said in a statement released Friday night. "At just 26, she has literally been around the world, with the simple but righteous goal of making it a better place. As long as there are humanitarians like Kayla in this world, evil will not prevail," the statement said. 
 
 Mueller told her town's local newspaper, The Daily Courier, she felt called to help those suffering the most in the midst of the Syrian conflict. 
 
 “For as long as I live, I will not let this suffering be normal,” she said in the May 2013 report. “[I will not let this be] something we just accept… It’s important to stop and realize what we have, why we have it and how privileged we are. And from that place, start caring and get a lot done.” 
 
 In October 2011, Mueller uploaded a video to a Syrian activist YouTube channel in which she said, “I am in solidarity with the Syrian people.” 
 
 ABC News' Nadine Shubailat, James Gordon Meek and Justin Fishel contributed to this report. ||||| She had always been the unidentified, lone female American hostage of the Islamic State. For nearly 17 months, while her fellow American captives were beheaded one after another in serial executions posted on YouTube, Kayla Mueller’s name remained a closely guarded secret, whispered among reporters, government officials and hostage negotiators — all fearing that any public mention might imperil her life. 
 
 On Friday, the Islamic State confirmed her identity, announcing that Ms. Mueller, a 26-year-old aid worker from Prescott, Ariz., had been killed in the falling rubble of a building in northern Syria that it said had been struck by bombs from a Jordanian warplane. Both the Jordanian and American governments said there was no proof, even as they rushed to deplore her possible death. Top Jordanian officials said the announcement was cynical propaganda. 
 
 But the group’s use of Ms. Mueller’s name for the first time prompted her family and its advisers to confirm her prolonged captivity in a statement and changed the calculus about what could be reported about her life. It threw a spotlight on a hostage ordeal that befell an eager and deeply idealistic young woman, who had ventured into one of the most dangerous parts of Syria — apparently without the backing of an aid organization, according to interviews with advisers to the family and employees of Doctors Without Borders, the international medical charity that hosted Ms. Mueller during her brief stay in one of Syria’s ravaged cities. 
 
 Continue reading the main story Kayla Mueller An online posting by the Islamic State showed a collapsed building in northern Syria where it said the 26-year-old woman had been killed. Ms. Mueller, 26, of Prescott, Ariz., is the last remaining American known to be held hostage by ISIS. 
 
 She was taken captive Aug. 4, 2013, in Aleppo, Syria. 
 
 She had worked with the humanitarian groups Support to Life and Danish Refugee Council, aiding Syrian refugees in Turkey. 
 
 A few months before she went missing, The Daily Courier in Arizona had profiled her work with refugee children. 
 
 Ms. Mueller participated in a “YouTube sit-in” organized by opponents of the Syrian government in 2011. 
 
 Initially based in southern Turkey, where she had worked for at least two aid organizations assisting Syrian refugees, Ms. Mueller appears to have driven into the northern Syrian city of Aleppo on Aug. 3, 2013, alongside a man who has been alternatively described as her Syrian friend or colleague, and by others as either her boyfriend or her fiancé. He had been invited to travel to the city to help fix the Internet connection for a compound run by the Spanish chapter of Doctors Without Borders, known in Spanish as Médicos Sin Fronteras, or M.S.F. Employees of the charity said they were surprised when the young Syrian man arrived with Ms. Mueller. 
 
 “On Aug. 3, 2013, a technician sent by a company contracted by M.S.F. arrived at one of the organization’s structures in Aleppo, Syria, to perform repairs. Unbeknown to the M.S.F. team, Kayla, a friend of the technician’s, was accompanying him,” said the group’s spokesman, Tim Shenk, in a statement. 
 
 It took longer than expected to finish the repair work, and as night approached, M.S.F. agreed to let the two stay overnight, out of concern for their safety, said Mr. Shenk. The next day the charity arranged to transport them to an Aleppo bus stop, where they planned to catch a bus back to Turkey. 
 
 They never made it. They were abducted on the road, the statement said. 
 
 Although Ms. Mueller had moved to Turkey in December 2012 to work with two organizations helping refugees — including the Danish Refugee Council — she was not employed by either of those groups when she entered Syria at a time when numerous foreigners already had been kidnapped inside the country, said the Mueller family advisers. What she was doing in Aleppo — beyond accompanying her Syrian companion — remains unclear. 
 
 Her companion, who was released after several months, declined to be interviewed. 
 
 “There is a lot of murkiness about what she was doing there. That’s been the problem — no one really knows,” said one adviser of the Muellers. 
 
 In the statement released Friday, the family said that it had received the first message from Ms. Mueller’s captors in May 2014 — nine months after her disappearance. The Islamic State, also known as ISIS or ISIL, provided initial proof that she was alive, the family said. 
 
 Then on July 12, 2014, the Islamic State announced that it would kill her within 30 days unless the family provided a ransom of 5 million euros ($5.6 million), or exchanged her for Dr. Aafia Siddiqui, a Pakistani scientist educated in America who was convicted of trying to kill American soldiers and F.B.I. agents in Afghanistan in 2008. She is serving a sentence in a Texas jail, according to an email explaining the demands forwarded to The New York Times by an acquaintance of the Muellers. When the deadline passed, nothing happened, prompting the family to hope that Ms. Mueller might be spared. 
 
 During those 30 days, her parents shared their ordeal only with the tight-knit group of advisers and with parents of other American hostages held by the Islamic State. Together the anxious parents traveled to Washington to meet Obama administration officials to push for the release of their children. That was shortly before the United States began airstrikes against the Islamic State in concert with European and Arab allies. Soon after, in August, the Islamic State posted the first of its decapitation videos, starting with the beheading of the American James Foley, and then in quick succession the fellow Americans Steven J. Sotloff and Peter Kassig. 
 
 A group of concerned advisers helping the Muellers dispatched negotiators to Turkey, Qatar, Lebanon and Iraq in an effort to find a way to contact the Islamic State to negotiate Ms. Mueller’s release. They spent many hours parsing messages by the Islamic State, trying to answer the crucial question: Would the group, which had shown no qualms about killing American male hostages, go so far as to behead a 26-year-old woman? 
 
 They feared the worst after the Islamic State released a video on Tuesday showing the immolation of a captured Jordanian pilot, a killing that shocked the world and particularly infuriated Jordan. In retaliation, the Jordanians then executed two prisoners convicted of terrorism, including a Qaeda-linked woman who had tried to blow up a hotel in Amman. 
 
 The Jordanians then began their own extensive bombings of Islamic State targets in Syria. 
 
 It was one of those attacks, the Islamic State said in its message Friday, that killed Ms. Mueller. 
 
 Experts on the Middle East said they believed Ms. Mueller was dead, since the Islamic State had no motivation to make such an assertion about a hostage if it were not true. Some also speculated that the Islamic State might have killed her beforehand and taken the opportunity to blame the Jordanian bombs in her death. 
 
 Andrew J. Tabler, senior fellow at the Program on Arab Politics at the Washington Institute for Near East Policy, said it was possible the militants “simply wanted to drive a wedge between regional and Western members of the coalition.” 
 
 Ms. Mueller, who was born in 1988, had a deep desire to help those less fortunate. After graduating from Northern Arizona University, she worked for aid organizations in India and Israel and in the occupied Palestinian territories, according to statement from her family. In 2012, she was drawn to what would soon become the world’s top humanitarian crisis, the Syrian civil war. She moved to Turkey, where many Syrians were seeking refuge, and she settled in a border town assisting Syrian families for the Danish Refugee Council and an aid group called Support to Life. “The common thread of Kayla’s life has been her quiet leadership and strong desire to serve others,” her family said in the statement. 
 
 The family advisers said there was not any indication that she had been working with an aid group when she went to Aleppo. She had no professional connection to the M.S.F. compound, said Carlos Francisco Cabello, the head of the Spanish section of Doctors Without Borders’ Syria mission. 
 
 “She appeared there with the external technician in a war zone. We didn’t know that she was coming, or otherwise we would not allow her to visit,” Mr. Cabello said, speaking by telephone from Turkey. “U.S. and U.K. citizens at that moment, and even now, were not considered for the Syrian mission for M.S.F. for obvious security reasons,” he said. 
 
 “She was never employed by M.S.F.-Spain in Syria. This must be clear,” he said, adding, “Aleppo at that time and now is a war zone.” 
 
 In an interview with The Daily Courier in Arizona, Ms. Mueller described how fulfilled she felt by her work with refugees, which included leading art classes for displaced Syrian children. 
 
 “For as long as I live, I will not let this suffering be normal,” she said.
– An incensed Jordan has been making good on its word to dole out "earth-shaking revenge" against ISIS, conducting airstrikes on militant outposts in Syria since a video was released earlier this week showing pilot Lt. Muath al-Kaseasbeh being burned alive in a cage. Now ISIS is claiming that a building that collapsed in Raqqa in one of those airstrikes was holding an American hostage—a woman who reportedly disappeared in August 2013 and was said to be ISIS' last remaining US captive, the New York Times reports. "The failed Jordanian aircraft killed an American female hostage," a message posted by the SITE Intelligence Group read today. "No mujahid [fighter] was injured in the bombardment, and all praise is due to Allah." The statement also names the hostage as Kayla Mueller. No evidence has been offered of her death yet, and a spokesperson for the White House National Security Council tells ABC the council has "not at this time seen any evidence that corroborates ISIL’s claim," using another acronym for the group. CNN cites a State Department spokesperson who says, "Obviously (we are) deeply concerned by these reports. We have not, at this point, seen anything that corroborates (ISIS's) claims." A Jordanian official calls the terror group's claim "illogical."