Possible mass graves near Mariupol shown in satellite images

New satellite images show apparent mass graves near Mariupol, where local officials accused Russia of burying up to 9,000 Ukrainian civilians to conceal the slaughter taking place in the ruined port city that's almost entirely under Russian control.

The images emerged just hours after Russian President Vladimir Putin on Thursday claimed victory in the battle for Mariupol, despite the presence of an estimated 2,000 Ukrainian fighters who were still holed up at a giant steel mill. Putin ordered his troops to seal off the stronghold "so that not even a fly comes through" instead of storming it.

Putin's decision to blockade the Azovstal steel plant likely indicates a desire to contain Ukrainian resistance in Mariupol and free up Russian forces to be deployed elsewhere in Eastern Ukraine, Britain's Defence Ministry said in an assessment Friday.

Satellite image provider Maxar Technologies released the photos, which it said showed more than 200 mass graves in a town where Ukrainian officials say the Russians have been burying Mariupol residents killed in the fighting. The imagery showed long rows of graves stretching away from an existing cemetery in the town of Manhush, outside Mariupol.

Mariupol Mayor Vadym Boychenko accused the Russians of "hiding their military crimes" by taking the bodies of civilians from the city and burying them in Manhush.

The graves could hold as many as 9,000 dead, the Mariupol City Council said Thursday in a post on the Telegram messaging app.

Boychenko labelled Russian actions in the city as "the new Babi Yar," a reference to the site of multiple Nazi massacres in which nearly 34,000 Ukrainian Jews were killed in 1941.

"The bodies of the dead were being brought by the truckload and actually simply being dumped in mounds," an aide to Boychenko, Piotr Andryushchenko, said on Telegram.

There was no immediate reaction from the Kremlin. When mass graves and hundreds of dead civilians were discovered in Bucha and other towns around Kyiv after Russian troops retreated three weeks ago, Russian officials denied that their soldiers killed any civilians there and accused Ukraine of staging the atrocities.

In a statement, Maxar said a review of previous images indicates that the graves in Manhush were dug in late March and expanded in recent weeks.

After nearly two lethal months of bombardment that largely reduced Mariupol to a smoking ruin, Russian forces appear to control the rest of the strategic southern city, including its vital but now badly damaged port.

But a few thousand Ukrainian troops, by Moscow's estimate, have stubbornly held out for weeks at the steel plant, despite a pummelling from Russian forces and repeated demands for their surrender. About 1,000 civilians were also trapped there, according to Ukrainian officials.

Ukrainian officials have repeatedly accused Russia of launching attacks to block civilian evacuations from Mariupol.

At least two Russian attacks on Thursday hit the city of Zaporizhzhia, a way station for people fleeing Mariupol. No one was wounded, the regional governor said.