(CNN) Around 3,800 civilians, almost a quarter of them children, have been killed in Russian airstrikes in Syria in the year since Russia began its air campaign there, according to a UK-based monitoring group. 

The Syrian Observatory of Human Rights released the stark figures to mark the first anniversary of Russia's direct intervention in support of Syrian President Bashar al-Assad's forces. 

According to figures collated by the group, Russian airstrikes killed 2,337 men, 906 children and 561 women in the past year. 

During the same period, it said, Russian warplanes killed 2,746 ISIS fighters, along with 2,814 rebels. 

CNN cannot independently confirm the figures. 

The activist group's grim toll comes as rebel-held districts of Aleppo reel from an intense weeklong aerial bombardment by Syrian and Russian warplanes while the Assad regime prepares to take the northern city. 

Sending a message to international community

In a statement, the group said Russia's actions had "increased the bloodshed of the Syrian people, which have made tens of thousands of them dead, injured or homeless." 

It said it was releasing the "shocking" statistics to "send a message to the international community" about the pain and suffering of the Syrian people. 

Russia and Syria maintain their military operations in Syria are directed at combating terrorism, a position US and UK diplomats have blasted at the United Nations in recent days. 

Russian Foreign Ministry spokeswoman Maria Zakharova reiterated that message Friday to Russian broadcaster Govorit Moskva, according to state-run Russian news outlet Sputnik. 

"In Syria, Russia is pursuing only one specific goal, it has been determined and announced -- it is the fight against the international terrorism," Sputnik quoted Zakharova as saying in a report on the anniversary of the Russian air campaign in Syria. 

An unnamed Syrian lieutenant, also quoted by Sputnik, said Russia's intervention had helped improve the situation. " Russian aircraft have brought Syrians hope for life and security," the lieutenant is cited as saying, adding that the Syrian army was closely coordinating with Russian forces. 

"In Latakia alone, dozens of villages were liberated in several months (after the Russian operation was launched).  Thousands of people returned to their homes." 

Kremlin spokesman Dmitry Peskov said Thursday that the Russian air force would continue its support of the Syrian armed forces. 

'Ultimate humanitarian shame'

The Syrian Observatory of Human Rights' casualty figures were released a day after a senior UN humanitarian affairs official condemned the international community's response to the crisis in Aleppo, where he says war crimes are being committed. 

The official, Stephen O'Brien, called the civil war the "ultimate humanitarian shame that is Syria today, and in east Aleppo in particular." 

O'Brien lambasted the inaction -- "be it through unwillingness or inability" -- of the international community to intervene in the crisis, which has escalated since the disintegration of a ceasefire last week. 

Repeating the accusations of UN Secretary-General Ban Ki-moon, O'Brien said the destruction of medical facilities in rebel-held eastern Aleppo and the use of "ever more destructive weapons" means that those using them "know they are committing war crimes." 

Photos: Heartbreaking images following Aleppo airstrike A Syrian family leaves the area following a reported airstrike on Friday, September 23, in rebel-held east Aleppo.  Following the airstrike, recovery teams from Syria Civil Defense, known as the White Helmets, began working to free the trapped and recover the dead, including small children.  Hide Caption 1 of 7 Photos: Heartbreaking images following Aleppo airstrike Hide Caption 2 of 7 Photos: Heartbreaking images following Aleppo airstrike This photo was released by the volunteer group Syria Civil Defense of the bodies of a man, with his knee pulled up near his face, and a child covered in dust after they were killed in the airstrike.  Hide Caption 3 of 7 Photos: Heartbreaking images following Aleppo airstrike The volunteers work to recover the bodies the man and child.  Hide Caption 4 of 7 Photos: Heartbreaking images following Aleppo airstrike A Syrian man carries the body of his nephew, recovered from the rubble.  Hide Caption 5 of 7 Photos: Heartbreaking images following Aleppo airstrike The volunteers remove an infant's body from the destroyed building.  Hide Caption 6 of 7 Photos: Heartbreaking images following Aleppo airstrike A Syrian woman carries the body of her infant after he was recovered.  Hide Caption 7 of 7

He said residents of the beleaguered city, particularly those in its eastern part, including 100,000 children, are "being subjected to deprivation, disease and death in increasing numbers and with increasing ferocity." 

"Let me be clear, east Aleppo this minute is not at the edge of the precipice, it is well into its terrible descent into the pitiless and merciless abyss of a humanitarian catastrophe unlike any we have witnessed in Syria, with no access by the UN since 7 July; and the health sector in east Aleppo is reportedly on the very verge of total collapse." 

He said that to engage in "political grandstanding" or to ignore "the horror unfolding before our eyes" would leave the UN Security Council "on the wrong side of history." 

Meanwhile, an estimated 10,000 Syrian-led troops have gathered in advance of what is believed to be perhaps a final ground assault by Syrian forces against rebels in Aleppo. 

This week's assault on rebel-held areas of the key city involved some of the worst violence since the start of the war in 2011.