Eastern Ukraine Fighting ‘Intensifying’Ukraine said Wednesday there was a preliminary agreement in place with Russia to evacuate civilians from the besieged city of Mariupol, while Russia again demanded the remaining Ukrainian troops there give up. Ukrainian Deputy Prime Minister Iryna Vereshchuk said the deal for a humanitarian corridor would allow women, children and the elderly to leave. "Given the catastrophic humanitarian situation in Mariupol, this is where we will focus our efforts today," Vereshchuk added in a Facebook post. Vereshchuk had reported three consecutive days of not being able to establish any humanitarian corridors in the country. SEE ALSO: Russia set a Wednesday deadline for Ukraine’s fighters to surrender in Mariupol, the latest in a series of ultimatums that Ukraine has rejected. A Tuesday deadline passed with Russia saying no Ukrainian troops accepted the offer to surrender in exchange for safety. The developments in Mariupol came as Russia continued to add to its military presence in the strategically important Donbas region. Britain’s defense ministry said Wednesday fighting in the region “is intensifying” as Russian forces tried to break through Ukraine’s defenses. "Russian attacks on cities across Ukraine show their intent to try and disrupt the movement of Ukrainian reinforcements and weaponry to the east of the country,” the ministry said. European Council President Charles Michel made an unannounced visit Wednesday to Kyiv, the latest show of support from European leaders who have traveled to Ukraine in recent weeks. “In Kyiv today. In the heart of a free and democratic Europe,” Michel tweeted. Hours earlier, Norway’s defense ministry announced a shipment of about 100 Mistral air defense missiles to Ukraine. A ministry statement said Norwegian forces were phasing out their own use of the missiles, but that they are a "modern and effective weapon" that will be useful for Ukrainian forces. White House press secretary Jen Psaki said U.S. President Joe Biden and the leaders of Britain, Canada, the European Commission, France, Germany, Italy, Japan, NATO, Poland and Romania spoke Tuesday about providing more ammunition and security assistance to Kyiv. Psaki said the United States is also considering imposing more economic sanctions this week. “There could be,” she said in response to that question. “I think that we're still ... making, doing considerations and running a process for additional sanctions, but there are some under consideration, yes.” Biden said NATO allies agreed Tuesday to release 240 million barrels of oil a day for the next six months, a move that he said would “help deny [Russian President Vladimir] Putin the ability to weaponize energy resources against American families and families in Europe and around the world.” Donbas offensive Russia declared Tuesday that it had launched its new offensive for control of eastern Ukraine with the bombardment of targets across the Donbas region, but Ukraine said it was defending the territory and repulsing some of the initial attacks. "Another phase of this operation is starting now," said Russian Foreign Minister Sergey Lavrov, adding that Moscow's goal was the "complete liberation" of the Donetsk and Luhansk territories in the east. In Washington, a senior Defense Department official called the new Russian military operations a "prelude" for bigger ones to come, saying, "There's a real possibility that this could go on for a while, because both sides can be fairly dug in here, and be dug in fairly well." The official said Ukraine is outmanned numerically compared to the Russian forces, but "that doesn't mean that they don't have advantages of their own or the ability to actively defend themselves," with weapons being "replenished every single day." Some segments of the $800 million U.S. tranche of military aid that Biden approved last week have already arrived in Ukraine. Pentagon spokesman John Kirby told reporters Tuesday that the United States is sending military aid in response to the situation on the ground. "You tailor each package based on the fight that they're in and what's going on at the time,” he said. “You also have to tailor your packages on what they can absorb on their end. … It would be irresponsible for us not to do it that way," Luhansk's governor said the eastern city of Kreminna is now "under the control" of Russian forces, which could allow Russia to advance on Kramatorsk, capital of the Donbas region. Humanitarian pause U.N. Secretary-General Antonio Guterres has called for a four-day cease-fire in Ukraine beginning Thursday to coincide with Orthodox Christians’ observance of Holy Week. SEE ALSO: Data from the U.N. refugee agency Wednesday showed the number of Ukrainian refugees who have fled the country surpassed 5 million. That is in addition to the 7 million people displaced within Ukraine. U.N. Deputy High Commission for Refugees Kelly Clements told the U.N. Security Council that an estimated 13 million more people are in the hardest hit areas of Ukraine, “many unable to move and difficult to reach with aid safely.” Carla Babb and Anita Powell contributed to this report. Some information also came from The Associated Press, Reuters and Agence France-Presse.