Mariupol appears close to falling under Russian control after a fierce battle for the key port city. The Russian defence ministry says it has cleared urban areas of Ukraine forces, and issued a 3am GMT “surrender or die” ultimatum to remaining defenders it says are trapped in a steelworks. If it falls, it would be Russia’s first seizure of a major city.

Ukraine president Volodymyr Zelenskiy has conceded the situation in Mariupol remains “extremely severe” but has not acknowledged it could fall. He warned peace talks would be scrapped if Russia killed the city’s remaining defenders. “The elimination of our troops, of our men (in Mariupol) will put an end to any negotiations,” he said.

Zelenskiy spoke on Saturday to the British prime minister, Boris Johnson, who praised the “bravery” of Ukraine’s defenders and promised to “continue to provide the means for Ukraine to defend itself”.

Russian billionaire Roman Abramovich has travelled to Kyiv in a bid to restart peace talks between Russia and Ukraine, according to Bloomberg. The report, based on unnamed sources, said Abramovich had met Ukrainian negotiators in an attempt to rescue the flagging talks.

Russia has resumed scattered missile attacks on Kyiv and western cities in Ukraine, with some civilian deaths reported in Kharkiv and in the capital. Russia had warned it would step up its missile bombardment following the sinking of its flagship missile cruiser Moskva.

The mayor of Irpin, on the western edge of Kyiv, says more than 70% of buildings in the town have been damaged or destroyed by Russian forces, according to the Kyiv Independent. In a Telegram post Oleksandr Markushin said a UN study based on satellite data showed 115 buildings were completely destroyed, 698 were significantly damaged, and 187 were partially damaged.

A forthcoming sixth round of EU sanctions on Russia will target oil and banks, in particular Sberbank, the head of the European Commission, Ursula von der Leyen, has told German newspaper Bild am Sonntag. The EU has so far spared Sberbank because it, along with Gazprombank, is one of the main channels for payments for Russian oil and gas.

Ukraine’s president warned that the world “needs to prepare” for the possibility of Russia using nuclear weapons. He told journalists in Kyiv “we shouldn’t wait for the moment” Russia used chemical or nuclear weapons. “[They] can use any weapon, I’m convinced of it,” he said.

Russia’s foreign ministry barred entry to the country for Johnson and other British government politicians and members in response to the government’s “hostile action” including sanctions. The Kremlin said it would expand restrictions against British politicians over what it calls a “wave of anti-Russian hysteria”.

The number of people evacuated from Ukrainian cities through humanitarian corridors dropped significantly on Saturday from the day before. A total of 1,449 people were evacuated, fewer than the 2,864 who escaped on Friday.

Pope Francis has condemned “the darkness and cruelty of war” in an Easter Saturday homily at the Vatican. Francis said his prayers were with four Ukraine politicians in the gathering, including the mayor of the occupied city of Melitopol, and “for all those suffering”.