Ukraine’s President Volodymyr Zelenskiy described Russia’s siege of Mariupol as “a terror that will be remembered for centuries to come,” while local authorities said thousands of residents had been forcibly relocated across the border.

“Several thousand Mariupol residents have been deported onto Russian territory in the last week,” the city council said late Saturday on its Telegram channel.

Russian news agencies have said buses have carried several hundred people Moscow calls refugees from Mariupol to Russia in recent days.

The council also said Russian forces bombed a Mariupol art school on Saturday in which 400 residents had taken shelter, but the number of casualties was not yet known.

Reuters could not independently verify the claims.

Russia denies targeting civilians.

Many of Mariupol’s 400,000 residents have been trapped for more than two weeks as Russia seeks to take control of the city, which would help secure a land corridor to the Crimea peninsula that Moscow annexed from Ukraine in 2014.

President Vladimir Putin calls the assault on Ukraine, which began on Feb. 24, a “special operation” aimed at demilitarising the country and rooting out people he terms dangerous nationalists.

Western nations call it an aggressive war of choice and have imposed punishing sanctions on Russia aimed at crippling its economy.

The Mariupol bombardment has left buildings in rubble and severed central supplies of electricity, heating and water, according to local authorities.

Rescue workers were still searching for survivors in a Mariupol theatre that local authorities say was flattened by Russian air strikes on Wednesday. Russia denies hitting the theatre.

Zelenskiy said the siege of Mariupol was a war crime. “To do this to a peaceful city… is a terror that will be remembered for centuries to come,” he said in a late night broadcast.

Still, he said, peace talks with Russia were needed although they were “not easy and pleasant”.