Russia has pounded targets in eastern Ukraine in a new offensive to take the country’s industrial heartland.

Cities in the Donbas came under Russian fire overnight, and the attacks interfered with efforts to evacuate civilians.

The Donbas is home to coal mines, metal plants and heavy-equipment factories and is bracing for what could be a decisive campaign.

On Thursday, Russian President Vladimir Putin claimed victory in the battle for the strategic southern port city of Mariupol, even though an estimated 2,000 Ukrainians remained holed up at a sprawling steelworks, which has been bombarded for weeks.

Mr Putin ordered his troops not to storm the stronghold but to seal it off.

At the same time, Maxar Technologies released new satellite images that it said showed more than 200 graves in a town near Mariupol, prompting accusations that the Russians were trying to conceal the slaughter of civilians taking place in the city.

Initial estimates from the Ukrainians said the graves could hold 9,000 bodies, but Petro Andryushchenko, an adviser to Mariupol’s mayor, said there could be more.

Ukrainian authorities have said over 20,000 civilians have been killed in the nearly two-month siege of Mariupol.

“The graves have been dug up and corpses are still being dumped there,” the mayor’s aide said.

Mr Putin said on Friday that Russia gave Ukrainian forces inside the steel plant the option to surrender, with guarantees to keep them alive, and offered “decent treatment and medical care,” according to an account of a phone call with European Council president Charles Michel, provided by the Kremlin.

“But the Kyiv regime does not allow them to take this opportunity,” Mr Putin charged.

Repeated attempts to evacuate civilians from the city have failed because Russia did not honour ceasefires, Ukrainian officials have said.

Ukrainian Deputy Prime Minister Iryna Vereshchuk said no humanitarian corridors for civilian evacuations would be open in Ukraine on Friday because it was too dangerous. She urged civilians to “be patient” and “hang in there”.

Days into the Russian offensive to take the east, the campaign has yet to become a full-out assault, with military analysts saying Moscow’s forces are still ramping up.

But scattered towns in the east have experienced the thud of incoming shells that drive citizens out in panic.

Slovyansk, a city of about 100,000 in eastern Ukraine, came under fire during the night, according to Mayor Vadym Lyakh, who said no injuries were reported.

But he urged residents to leave and said a convoy of buses would be organised. In Rubizhne, Russian fire prevented attempts to bring buses in, Luhansk Governor Serhiy Haidai said.

Intensive shelling was also heard overnight in Kharkiv, a north-eastern city that lies outside of the Donbas but is seen as one of the gateways the Russians intend to use to encircle Ukrainian forces in the Donbas from the north, the south and the east.

If successful, the campaign would give Mr Putin a vital piece of the country and a badly needed victory to show the Russian people amid the war’s mounting casualties and the economic hardship caused by Western sanctions.

But analysts say Russian forces have yet to achieve any major breakthroughs in the Donbas or gain any significant ground.

A senior US defence official, speaking on condition of anonymity to discuss the Pentagon’s assessment, said the Ukrainians were hindering the Russian effort to push south from Izyum, which lies outside the Donbas.

On Friday, Rustam Minnekayev, a senior Russian military official, outlined Russian war aims that appeared to be wider than what the Kremlin has stated in recent weeks. He said Russia’s forces aim to take full control of not just eastern Ukraine but southern Ukraine too.

He said such a move would open the way to the nation of Moldova, where Russia backs the breakaway region of Transnistria. Moldovan officials are warily watching Mr Putin’s actions in Ukraine.

Meanwhile, Russia’s top diplomat, Foreign Minister Sergei Lavrov, said talks between the two countries have “ground to a halt” because Moscow has not received a response from Kyiv to its latest proposals, the details of which have not been released.

Mr Putin’s lead negotiator at the talks, Vladimir Medinsky, said he held several lengthy conversations on Friday with the head of the Ukrainian delegation. He gave no details on what was discussed or say if any progress was made.

The battle for Mariupol has been seen as key to the eastern assault. Its capture would complete a land bridge between Russia and the Crimean Peninsula, which was seized by Moscow in 2014, and free up Mr Putin’s forces to take part in the larger campaign in the east.