Russia Launches New Attacks on MariupolRussia launched new attacks Wednesday on the embattled Ukrainian port city of Mariupol, even as local officials tried to create a humanitarian corridor for women, children and older adults to escape west to the Ukrainian-controlled city of Zaporizhzhia. Moscow's forces bombed the sprawling Azovstal steel plant, where the last Ukrainian fighters were holed up and ignoring Russian demands to lay down their arms and surrender. More than 100,000 people were believed trapped in the city on the north coast of the Sea of Azov, where 400,000 lived before Russia invaded the country February 24. "The conditions there are truly horrific," U.S. Secretary of State Antony Blinken said at a diplomatic conference in Panama. He underscored that attempted humanitarian corridors to allow Mariupol residents to escape "have fallen apart very quickly." Ukrainian Deputy Prime Minister Iryna Vereshchuk said there was a preliminary agreement to open a humanitarian corridor through which women, children and older adults could leave, and Mariupol Mayor Vadym Boychenko urged residents to take advantage of it. "Do not be frightened, and evacuate to Zaporizhzhia, where you can receive all the help you need — food, medicine, essentials — and the main thing is that you will be in safety," the mayor said in a statement. SEE ALSO: Russia estimates that a few thousand Ukrainian troops remain holed up in the steel plant. Kyiv's forces have ignored several Russian demands to surrender and exit the plant's labyrinth of tunnels and bunkers. The fight over Mariupol is part of a broader Russian offensive to take control over mostly Russian-speaking eastern Ukraine, home to coal mines and heavy-equipment factories vital to Ukraine's economy. But Ukraine, buoyed by new shipments of arms from the U.S. and its Western allies, has vowed to not give up the region and is engaged in heavy warfare with the Russians. U.S. Defense Department analysts say the battle for the Donbas region, where fighting has been ongoing for eight years, could last for months more. U.S. President Joe Biden last week approved an $800 million shipment of more weaponry for Ukraine and now is expected to announce another package in the coming days that will include additional artillery. Canada and the Netherlands also said they would send more heavy weapons. 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 that 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 that Norwegian forces were phasing out the missiles but that they were a "modern and effective weapon" that Ukrainian forces would find useful. 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: Guterres also said he has written to Russian President Vladimir Putin and Ukrainian President Volodymyr Zelenskyy, asking them to meet with him in their respective capitals as he seeks a diplomatic solution to the war. Data from the U.N. refugee agency Wednesday showed that 5 million Ukrainian refugees have now fled the country because of the war and another 7 million have been displaced within the country. U.N. Deputy High Commissioner for Refugees Kelly Clements told the U.N. Security Council that an estimated 13 million more people were in the hardest hit areas of Ukraine, many of whom were "unable to move and difficult to reach with aid safely." Some information for this report came from The Associated Press, Reuters and Agence France-Presse.