More than 1000 Ukrainian marines have surrendered in the port of Mariupol, Russia’s defence ministry says of its main strategic target in the eastern Donbas region, which has been reduced to ruins but not yet under Russian control.

If the Russians take the Azovstal industrial district, where the marines have been holed up, they would be in full control of Mariupol, Ukraine’s main Sea of Azov port, allowing Russia to reinforce a land corridor between separatist-held eastern areas and the Crimea region that it seized and annexed in 2014.

Surrounded and bombarded by Russian troops for weeks and the focus of some of the fiercest fighting of the war, Mariupol would be the first major city to fall since Russia invaded Ukraine on February 24.

Russia’s defence ministry on Wednesday said that 1026 marines had surrendered, including 162 officers.

Ukraine’s general staff said Russian forces were proceeding with attacks on Azovstal and the port, but a defence ministry spokesman said he had no information about any surrender.

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 Zelensky 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.

Russian TV 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 Defence Minister Hanna Malyar has said there was a high risk of Russia using chemical weapons in their assault on the country, echoing earlier warnings by Mr Zelenskiy, who on Wednesday told the Estonian parliament by videolink Russia was using phosphorus bombs to terrorise civilians.

Moscow’s 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 general’s 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.

The presidents of Poland, Lithuania, Latvia and Estonia arrived in Kyiv to meet Mr Zelenskiy, the Polish leader’s office said.

Estonian President Alar Karis had earlier tweeted that they were offering political support and military aid.

US President Joe Biden said for the first time that Moscow’s invasion of Ukraine amounted to genocide, as Mr Putin said Russia would “rhythmically and calmly” continue its operation and achieve its goals.

An initial report by a mission of experts set up by Organisation for Security and Co-operation in Europe documents a “catalogue of inhumanity” by Russian troops in Ukraine, the US ambassador to the OSCE said.

“This includes evidence of direct targeting of civilians, attacks on medical facilities, rape, executions, looting and forced deportation of civilians to Russia,” Michael Carpenter said in a statement.

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.