Russia on Tuesday claimed it had opened humanitarian corridors for soldiers who voluntarily surrendered from Mariupol’s Azovstal steel plant – a site of refuge and resistance for Ukrainian fighters.

 "Taking into account the catastrophic situation at the Azovstal metallurgical plant in the city of Mariupol, as well as being guided by purely humane principles, the Russian Armed Forces have opened a humanitarian corridor for the withdrawal of Ukrainian servicemen and fighters of nationalist formations who voluntarily laid down arms," Colonel General Mikhail Mizintsev, head of the Russian National Defense Management Center said. 

Servicemen of the Donetsk People's Republic militia look at bodies of Ukrainian soldiers placed in plastic bags in a tunnel, part of the Illich Iron & Steel Works Metallurgical Plant, the second largest metallurgical enterprise in Ukraine, in an area controlled by Russian-backed separatist forces in Mariupol, Ukraine, Monday, April 18, 2022. Mariupol, a strategic port on the Sea of Azov, has been besieged by Russian troops and forces from self-proclaimed separatist areas in eastern Ukraine for more than six weeks.  (AP Photo/Alexei Alexandrov)

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The claim comes just hours after Moscow set a deadline for noon local time – 5 a.m. EDT – calling on all forces bunkered in the Azovstal Iron and Steel Works plant to surrender "without exception, without any weapons and without ammunition."

The steel factory, once the site of one of Europe’s largest metallurgical plants, has become a stronghold for the resistance who have relied on a deep network of tunnels to house civilians and resistance forces alike. 

It is unclear if any Ukrainian fighters voluntarily surrendered to the Russian forces.

But Ukrainian Deputy Prime Minister Iryna Vereshchuk said that there had been no such agreement made with the Russian forces and noted that four people were killed when trying to evacuate Mariupol on Tuesday. 

Smoke rises above Azovstal steelworks, in Mariupol, Ukraine, in this still image obtained from a recent drone video posted on social media.  (MARIUPOL CITY COUNCIL/via REUTERS  THIS IMAGE HAS BEEN SUPPLIED BY A THIRD PARTY. MANDATORY CREDIT. NO RESALES. NO ARCHIVES.)

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Ukrainian commander of the Azov Regiment, Denys Prokopenko, said Monday that Russian forces had been targeting the steel plant by pummeling it with bunker-buster bombs. 

Moscow announced Tuesday that it had begun its second campaign in eastern Ukraine – a strategy defense officials have warned against for weeks after Russian forces failed to take Kyiv. 

The Mariupol city council alleged on Telegram Tuesday that Russian forces were preparing to drop a three-ton "surprise" from the sky, but details on the forewarned bombardment remain unknown.

A view of the Mariupol theater damaged during fighting in Mariupol, in territory under the government of the Donetsk People's Republic, eastern Ukraine, Monday, April 4, 2022. 

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An estimated 120,000 people are still in Mariupol who have been unable to evacuate following weeks of failed humanitarian corridor agreements and constant shelling by Russian forces. 

Mariupol Mayor Vadym Boychenko said last week that the siege has killed more than 20,000 civilians since the invasion began in late February. 

Greg Headen contributed to this report.