More than a thousand Ukrainian marines have surrendered in the besieged Ukrainian port of Mariupol, Russia’s defence ministry said on Wednesday of Moscow’s main target in the eastern Donbas region which it has yet to bring under its control.

If the Russians seize the Azovstal industrial district, where the marines have been holed up, they would be in full control of Mariupol, the lynchpin between Russian-held areas to the west and east providing a land corridor for troops and supplies.

It would be the first major city to fall to Russian forces since they invaded Ukraine on Feb. 24.

Ukraine’s general staff said that Russian forces were proceeding with attacks on Azovstal and the port. Ukraine’s 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.

Thousands are believed to have been killed under a near-seven week siege of 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 that city with no way to bring in food or water, and accuses Russia of blocking aid convoys.

Russia’s defence ministry said that 1,026 soldiers of Ukraine’s 36th Marine Brigade surrendered.

Chechen leader Ramzan Kadyrov, an ardent supporter of Russian President Vladimir Putin, urged remaining Ukrainian 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.