With Russia claiming to have taken prisoner nearly 2,500 Ukrainian fighters from the besieged Mariupol steel plant, concerns grew about their fate as a Moscow-backed separatist leader vowed they would face tribunals. Russia has declared its full control of the Azovstal steel plant, which for weeks was the last holdout in Mariupol and a symbol of Ukrainian tenacity in the strategic port city, now in ruins with more than 20,000 residents feared dead. The seizure gives Russian President Vladimir Putin a badly wanted victory in the war he began nearly three months ago. The Russian Defence Ministry released video of Ukrainian soldiers being detained after announcing that its forces had removed the last holdouts from the Mariupol plant’s extensive underground tunnels. It said a total of 2,439 had surrendered. Russia claims to have taken full control of Ukraine’s Mariupol Family members of the fighters, who came from a variety of military and law enforcement units, have pleaded for them to be given rights as prisoners of war and eventually returned to Ukraine. Deputy Prime Minister Iryna Vereshchuk said Saturday that Ukraine “will fight for the return” of every one of them. Denis Pushilin, the pro-Kremlin head of an area of eastern Ukraine controlled by Moscow-backed separatists, said the captured fighters included some foreign nationals, though he did not provide details. He said they were sure to face a tribunal. Russian officials and state media have sought to characterise the fighters as neo-Nazis and criminals. “I believe that justice must be restored. There is a request for this from ordinary people, society, and, probably, the sane part of the world community,” Russian state news agency Tass quoted Pushilin as saying. Who were Mariupol’s last defenders? The Ukrainian government has not commented on Russia’s claim of capturing Azovstal. Ukraine’s military had told the fighters their mission was complete and they could come out. It described their extraction as an evacuation, not a mass surrender. The capture of Mariupol furthers Russia’s quest to create a land bridge from Russia stretching through the Donbas region to the Crimean Peninsula, which Moscow seized from Ukraine in 2014. The impact on the broader war remained unclear. Many Russian troops already had been redeployed from Mariupol to elsewhere in the conflict. The Ukrainian military reported heavy fighting in much of the Donbas in eastern Ukraine. “The situation in Donbas is extremely difficult,” President Volodymyr Zelensky said in his nightly video address to the nation. “As in previous days, the Russian army is trying to attack Sloviansk and Sievierodonetsk.” He said Ukrainian forces are delaying the offensive “every day.” Sievierodonetsk is the main city under Ukrainian control in the Luhansk region, which together with the Donetsk region makes up the Donbas. Governor Serhii Haidai said the only functioning hospital in the city has just three doctors and supplies for 10 days. Sloviansk, in the Donetsk region, is critical to Russia’s objective of capturing all of eastern Ukraine and saw fierce fighting last month after Moscow’s troops backed off from Kyiv. Russian shelling on Saturday killed seven civilians and injured 10 more elsewhere in the region, the Governor said. Zelensky on Saturday emphasised that the Donbas remains part of Ukraine and his forces were fighting to liberate it. Mariupol, which is part of the Donbas, was blockaded early in the war and became a frightening example to people elsewhere in the country of the hunger, terror and death they might face if the Russians surrounded their communities. An estimated 100,000 of the 450,000 people who were living in Mariupol before the war remain. Many, trapped by Russia’s siege, were left without food, water and electricity. The Ukrainian mayor of Mariupol warned on Saturday the city is facing a health and sanitation “catastrophe” from mass burials in shallow pits across the ruined city as well as the breakdown of sewage systems. Vadim Boychenko said summer rains threaten to contaminate water sources as he pressed Russian forces to allow residents to safely leave the city. “In addition to the humanitarian catastrophe created by the [Russian] occupiers and collaborators, the city is on the verge of an outbreak of infectious diseases,” he said on the messaging app Telegram.