Nearly 700 more Ukrainian fighters have surrendered at the Mariupol steelworks in the past 24 hours, Russia says, but leaders were reported to still be holed up inside, delaying the final end of Europe's longest and bloodiest battle for decades.
Finland and Sweden meanwhile formally applied to join NATO, bringing about the very expansion that Russian President Vladimir Putin has long cited as one of his main reasons for launching the "special military operation" in February.
Russia's ministry of defence said the Wednesday surrender of 694 more fighters meant a total of 959 people had now lain down their arms at the vast Azovstal steelworks, the last bastion of Ukrainian defenders in the city.
If confirmed, the Russian announcement would resolve much of the mystery surrounding the fate of hundreds of fighters inside the plant, since Ukraine announced on Tuesday it had ordered the entire garrison to stand down. The Ukrainian defence ministry, which has so far confirmed only about 250 having left the plant, did not immediately respond to a written request for comment.
The leader of pro-Russian separatists in control of the area was quoted by a local news agency as saying the main commanders inside the plant had yet to surrender: "They have not left", DAN news agency quoted Denis Pushilin as saying.
The final surrender of Mariupol would bring a close to a near three month siege of the once prosperous city of 400,000 people, where Ukraine says tens of thousands of civilians died under Russian siege and bombardment, many buried in mass graves.
Kyiv and Moscow had both said on Tuesday that about 250 people left the plant, giving little clue as to the fate of hundreds more believed to be inside. Ukraine said it would not reveal how many were there until the operation to rescue all of them was complete.
Ukrainian officials have spoken of hopes to arrange a prisoner swap for Mariupol defenders they describe as national heroes. Moscow says no such deal was made for fighters it calls Nazis.
Russia said more than 50 wounded fighters have been brought for treatment to a hospital, and others have been taken to a newly re-opened prison, both in towns held by pro-Russian separatists. Reuters journalists have filmed buses bringing captured fighters to both locations.
The Kremlin said Putin has personally guaranteed the humane treatment of those who surrender, but high-profile Russian politicians have publicly called for them never to be exchanged, or even for their execution.
The Swedish and Finnish ambassadors handed over their NATO membership application letters in a ceremony at the alliance's headquarters.
"This is a historic moment, which we must seize," NATO Secretary-General Jens Stoltenberg said.
Ratification of all 30 allied parliaments could take up to a year, diplomats say. Turkey has surprised its allies in recent days by saying it had reservations about the new prospective members, especially their tolerance of Kurdish militant groups on their soil.
The steelworks surrender in Mariupol allows Putin to claim a rare victory in a campaign which has otherwise faltered. Recent weeks have seen Russian forces abandon the area around Ukraine's second larges city Kharkiv, now retreating at their fastest rate since they were driven from the north and the Kyiv environs at the end of March.
Nevertheless, Moscow has continued to press on with its main offensive, trying to capture more territory in the Donbas region of southeastern Ukraine which it claims on behalf of separatists it has supported since 2014.
Mariupol, the main port for the Donbas, is the biggest city Russia has captured so far, and gives Moscow full control of the Sea of Azov and an unbroken swathe of territory across the east and south of Ukraine.
The siege was the deadliest battle in Europe at least since the wars in Chechnya and the Balkans of the 1990s.
The city's months of resistance became a global emblem of Ukraine's refusal to yield against a far better-armed foe, while its near total destruction demonstrated Russia's tactic of raining down fire on population centres.
Russia insists it had agreed to no prisoner swap in advance for the Azovstal defenders, many of whom belong to the Azov Regiment, a Ukrainian unit with origins as a far right militia, which Russia describes as Nazis and blames for mistreating Russian speakers.
Australian Associated Press
Sign up for our newsletter to stay up to date.