MARIUPOL, Ukraine: More than 250 Ukrainian fighters surrendered to Russian forces at the Azovstal steelworks in Mariupol and Kyiv said on Tuesday it had ordered its full garrison to evacuate, bringing an apparent end to the bloodiest battle in Europe for decades.

Reuters saw buses leave the steelworks overnight and five of them arrive in the Russian-held town of Novoazovsk, where Moscow said the wounded would be treated.

In one, marked with the Latin letter ‘Z’ that symbolises Russia’s assault, wounded men were stacked on stretchers three bunks high. One man was wheeled out, his head tightly wrapped in thick bandages.

While both sides spoke of a deal under which all Ukrainian troops would abandon the huge steelworks, important details were not yet public, including how many fighters still remained inside, and whether any form of prisoner swap had been agreed.

Ukraine’s Deputy Defence Minister Hanna Malyar told a briefing that Kyiv would not disclose how many fighters were inside the plant until all were safe.

The Kremlin said President Vladimir Putin had personally guaranteed the prisoners would be treated according to international standards.

“The ‘Mariupol’ garrison has fulfilled its combat mission,” the General Staff of Ukraine’s Armed Forces said in a statement.

“The supreme military command ordered the commanders of the units stationed at Azovstal to save the lives of the personnel.”

In a television address, President Volodymyr Zelenskiy said: “Ukraine needs Ukrainian heroes alive.”

Russian defence ministry video showed fighters leaving the plant in daylight, some carried on stretchers, others with hands up to be searched by Russian troops.

Russia said at least 256 Ukrainian fighters had “laid down their arms and surrendered”, including 51 severely wounded. Ukraine said 264 soldiers, including 53 wounded, had left.

Ruins

The surrender appears to mark the end of the battle of Mariupol, where Ukraine believes tens of thousands of people were killed under months of Russian bombardment and siege.

The city now lies in ruins. Its complete capture is Russia’s biggest victory of the war, giving Moscow total control of the coast of the Sea of Azov and an unbroken stretch of eastern and southern Ukraine.

But it comes as Russia’s campaign has faltered elsewhere, with troops retreating from the outskirts of Kharkiv in the northeast at the fastest pace since they were driven from the north and outskirts of Kyiv at the end of March.

Authorities on both sides gave few clues about the ultimate fate of Mariupol’s last defenders. Ukraine’s Deputy Prime Minister Iryna Vereshchuk said Kyiv aimed to arrange a prisoner swap for the wounded once their condition stabilises, but neither side disclosed terms for any specific deal.

Natalia, wife of a sailor among those holed up in the plant, told Reuters she hoped “there will be an honest exchange”. But she was still worried: “What Russia is doing now is inhumane.”

Victory

Mariupol is the biggest city Russia has captured since its Feb. 24 invasion, giving Moscow a clear-cut victory for the first time in months.

In a statement on Monday, the Azov Regiment, the main Ukrainian unit that had held out in the steelworks, said it had achieved its objective over 82 days of resistance by making it possible to defend the rest of the country.

The regiment, now part of Ukraine’s territorial defence forces, originated as a far-right militia, and Moscow has portrayed defeating its fighters as central to its stated objective of “de-Nazifying” Ukraine. Russia blames them for mistreating Russian speakers, one of its war justifications, which Kyiv and its Western backers call a bogus pretext.

High-profile Russian lawmakers spoke out against any prisoner swap. Vyacheslav Volodin, speaker of the State Duma, Russia’s lower house, said: “Nazi criminals should not be exchanged.” Lawmaker Leonid Slutsky, one of Russia’s negotiators in talks with Ukraine, called the evacuated combatants “animals in human form” and said they should be executed.

The United Nations and Red Cross say thousands of Ukrainian civilians died under Russia’s siege of the port of 400,000 people, with the true toll uncounted but certain to be Europe’s worst since the 1990s wars in Chechnya and the Balkans.

For months, Mariupol’s residents were driven into cellars under perpetual bombardment, with no access to food, fresh water or heat, and bodies littering the streets. Two strikes - on a maternity ward and a theatre where hundreds of people were sheltering - became worldwide emblems of Russia’s tactic of devastating population centres.

Thousands of civilians are believed to have been buried in mass graves or makeshift pits in gardens, and Ukraine says Moscow forcibly deported thousands of residents to Russia.

Moscow denies targeting civilians or deporting them.

Ukraine advances

Elsewhere, Ukrainian forces have been advancing at their fastest pace for more than a month, driving Russian forces out of the area around Kharkiv, Ukraine’s second largest city.

Ukraine says its forces had reached the Russian border, 40 km north of Kharkiv. They have also pushed at least as far as the Siverskiy Donets river 40 km to the east, where they could threaten supply lines to Russia’s main advance in the Donbas.

Russia is still pressing that advance, despite taking heavy losses.

Finland and Sweden have announced plans to join NATO, bringing about the very expansion of the Western alliance Putin invoked as one of the main justifications for his “special military operation”. U.S. President Joe Biden was due to host the Swedish and Finnish leaders at the White House on Thursday.

After weeks in which Russia threatened unspecified retaliation, Putin said on Monday Russia had “no problems” with either country, and their NATO membership would be an issue only if the alliance deployed additional troops or weapons.

Foreign Minister Sergei Lavrov said on Tuesday there would be “probably not much difference” if Finland and Sweden joined NATO since they had already participated in alliance drills.