More than 1,000 Ukrainian marines have surrendered in the besieged port of Mariupol, Russias defense ministry said on Wednesday of Moscows main target in the eastern Donbas region which it has yet to bring under its control. If the Russians take the Azovstal industrial district, where the marines have been holed up, they would be in full control of Mariupol, which would allow Russia to reinforce a land corridor between separatist-held eastern areas and the Crimea region that it seized and annexed in 2014. Surrounded by Russian troops for weeks, Mariupol would be the first major city to fall since Russia invaded Ukraine on Feb. 24, with the battle for the industrial heartland of Donbas likely to define the course of the war. Ukraines general staff said that Russian forces were proceeding with attacks on Azovstal and the port, but a defence ministry spokesman said he had no information about any surrender. Reuters journalists accompanying Russian-backed separatists saw flames billowing from the Azovstal district on Tuesday. On Monday, the 36th Marine Brigade said it was preparing for a final battle in Mariupol that would end in death or capture as its troops had run out of ammunition. Thousands of people are believed to have been killed in Mariupol and Russia has been massing thousands of troops in the area for a new assault, Ukrainian President Volodymyr Zelenskiy said. Ukraine says tens of thousands of civilians have been trapped inside the city with no way to bring in food or water, and accuses Russia of blocking aid convoys. Russias defense ministry said that 1,026 soldiers of Ukraines 36th Marine Brigade surrendered, including 162 officers. Chemical weapons warning Chechen leader Ramzan Kadyrov, an ardent supporter of Russian President Vladimir Putin, urged remaining Ukrainians holed up in Azovstal to surrender. "Within Azovstal at the moment there are about 200 wounded who cannot receive any medical assistance," Kadyrov said in a Telegram post. "For them and all the rest it would be better to end this pointless resistance and go home to their families." Russian television showed pictures of what it said were marines giving themselves up at Illich Iron and Steel Works in Mariupol on Tuesday, many of them wounded. It showed what it said were Ukrainian soldiers being marched down a road with their hands in the air. One of the soldiers was shown holding a Ukrainian passport. Ukrainian Deputy Defense Minister Hanna Malyar has said there was a high risk of Russia using chemical weapons, echoing earlier warnings by Zelenskiy, who on Wednesday told the Estonian parliament by videolink Russia was using phosphorus bombs to terrorize civilians. He did not provide evidence and Reuters has not been able to independently verify his assertion. Chemical weapons production, use and stockpiling is banned under the 1997 Chemical Weapons Convention. Although condemned by human rights groups, white phosphorous is not banned. Russia denies using chemical weapons, saying it had destroyed its last chemical stockpiles in 2017. Moscows incursion into Ukraine, the biggest attack on a European state since 1945, has seen more than 4.6 million people flee abroad, killed or wounded thousands and left Russia increasingly isolated on the world stage. The Ukrainian prosecutor generals office said 191 children had been killed and 349 wounded since the start of the invasion. The Kremlin says it launched a "special military operation" to demilitarise and "denazify" Ukraine. Kyiv and its Western allies reject that as a false pretext for an unprovoked attack. Four presidents visiting Kyiv The presidents of Poland, Lithuania, Latvia and Estonia were on their way to Kyiv to meet Zelenskiy, an adviser to the Polish leader said on Wednesday. The four join a growing number of European politicians to visit the Ukrainian capital since Russian forces were driven away from the countrys north earlier this month. US President Joe Biden said for the first time that Moscows invasion of Ukraine amounted to genocide, as Putin said Russia would "rhythmically and calmly" continue its operation and achieve its goals. Russia has denied targeting civilians and has said Ukrainian and Western allegations of war crimes are fabricated. Many towns Russia has retreated from in northern Ukraine were littered with the bodies of civilians killed in what Kyiv says was a campaign of murder, torture and rape. Interfax Ukraine news agency on Wednesday quoted the Kyiv district police chief saying 720 bodies had been found in the region around the capital, with more than 200 people missing. The General Headquarters of the Armed Forces of Ukraine said Russian forces were maintaining attacks on civilian infrastructure in the Kharkiv region in the northeast and the Zaporizhzhia region in central Ukraine. At least seven people were killed and 22 wounded in Kharkiv over the past 24 hours, Governor Oleh Synegubov said. A 2-year-old boy was among those killed in the 53 artillery or rocket strikes Russian forces had carried out in the region, he said in an online post. Reuters could not independently verify the information. Russia denies targeting civilians. Putin on Tuesday used his first public comments on the conflict in more than a week to say Russia would "rhythmically and calmly" continue its operation, and expressed confidence his goals would be achieved. Zelenskiy mocked Putin in an early morning address: "How could a plan that provides for the death of tens of thousands of their own soldiers in a little more than a month of war come about?"