New operation to evacuate Mariupol civilians has begun, says Ukraine

Russia denies any plan to use nuclear weapons in Ukraine

Ukraine said a new attempt was underway on Friday to evacuate scores of civilians trapped in a heavily bombed steel works in the city of Mariupol, after bloody fighting with Russian forces thwarted efforts to bring them to safety the previous day.

Mariupol, a strategic southern port on the Azov Sea, has endured the most destructive siege of the 10-week-old war and the sprawling Soviet-era Azovstal steel plant is the last part of the city still in the hands of holdout Ukrainian fighters.

U.N.-brokered evacuations of some of the hundreds of civilians who had taken shelter in the plant's network of tunnels and bunkers began at the weekend, but were halted in recent days by renewed fighting.

"The next stage of rescuing our people from Azovstal is underway at the moment. Information about the results will be provided later," said Andriy Yermak, head of the Ukrainian presidential staff. He gave no more details.

On the other hand, Russian foreign ministry spokesman Alexei Zaitsev said on Friday that Russia will not use nuclear weapons in Ukraine.

Zaitsev told reporters the use of nuclear weapons by Russia - a risk that Western officials have publicly discussed - was not applicable to what Moscow calls its special military operation in Ukraine.

Russia has turned its heaviest firepower on Ukraine's east and south, after failing to take the capital Kyiv in the early weeks following its Feb. 24 invasion. The new front is aimed at limiting Ukraine's access to the Black Sea, vital for its grain and metals exports, and linking Russian-controlled territory in the east to the Crimea Peninsula, seized by Moscow in 2014.