Russian forces have struck targets across Ukraine's eastern Donetsk region to prepare the path for an expected armoured push to try to take more territory as the five-month-old war entered a new phase.

The strikes, reported by the region's local governor and the Russian military, followed Moscow's capture of the Ukrainian city of Lysychansk on Sunday, a move that handed it total control of the Luhansk region, one of its main war aims.

Taking full control of Donetsk, the other region in Donbas, the industrialised eastern part of Ukraine that has become the stage of the biggest battle in Europe in generations, is another goal of what Moscow calls its "special military operation."

Ukrainian forces which retreated from Lysychansk at the weekend have taken up new defensive lines in Donetsk, according to Serhiy Gaidai, the Ukrainian governor of Luhansk.

In a foretaste of what is likely to follow, Pavlo Kyrylenko, the governor of neighbouring Donetsk, said on television that his region had been hit overnight.

"Sloviansk and Kramatorsk came under shelling. They are now also the main line of assault for the enemy from the Lyman direction... there is no safe place without shelling in the Donetsk region," he said.

Russian tanks in the city of Lysychansk

The Russian defence ministry, which says it does not target residential areas, said it had used what it called high-precision weapons to destroy command centres and artillery in Donetsk, where Ukraine still controls major cities.

President Vladimir Putin has told troops involved in capturing Luhansk who would also be part of any attempt to capture cities in Donetsk, to "rest and recover their military preparedness", while units in other parts of Ukraine keep fighting.

Both sides have suffered heavy casualties in the fight for Luhansk, particularly during the siege of the twin cities of Lysychansk and Sievierodonetsk. Both have been left wrecked.

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A Reuters reporter who visited Lysychansk yesterday found widespread destruction and few residents in a city that was once home to nearly 100,000 people.

Those who were left surveyed bullet-riddled up-ended Ukrainian police cars, hulking local government buildings scorched by shell fire and the damaged golden dome of an Orthodox church.

Since the outset of the conflict, Russia has demanded that Ukraine hand both Luhansk and Donetsk to Moscow-backed separatists, who have declared their independence.

"This is the last victory for Russia on Ukrainian territory," Oleksiy Arestovych, adviser to President Volodymyr Zelensky, said in a video posted online.

"These were medium-sized cities. And this took from 4th April until 4th July - that's 90 days. So many losses."

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Mr Arestovych said besides the battle for Donetsk, Ukraine was hoping to launch counter offensives in the south of the country.

"Taking the cities in the east meant that 60% of Russian forces are now concentrated in the east and it is difficult for them to be redirected to the south," he said.

"And there are no more forces that can be brought in from Russia. They paid a big price for Sievierodonetsk and Lysychansk."

Lysychansk has been destroyed by shelling

Some military experts reckoned the hard fought victory had brought Russian forces little strategic gain, and the outcome of what has been dubbed the "battle of the Donbas" remained in the balance.

"I think it's a tactical victory for Russia but at an enormous cost," said Neil Melvin of the RUSI think tank in London. He compared the battle to the huge fights for meagre territorial gains that characterised World War I.

"The Russians may declare some kind of victory, but the key war battle is still yet to come," he said.

He said the decisive battle for Ukraine was likely to be fought not in the east, where Russia is mounting its main assault, but in the south, where Ukraine has begun a counter-offensive to recapture territory around the city ofKherson.

"There are counter-attacks beginning there and I think it's most likely that we'll see the momentum swing to Ukraine as ittries to then mount a large-scale counter-offensive to push the Russians back," he said.

Earlier, Russian rockets hit Mykolaiv, a southern city on the main highway between Kherson and Odesa, the mayor, Oleksandr Senkevych, said.

Mr Zelensky said last night that despite Ukraine's withdrawal from Lysychansk, its troops continued to fight.

"The armed forces of Ukraine respond, push back and destroy the offensive potential of the occupiers day after day," Mr Zelensky said in a nightly video message.

"We need to break them. It is a difficult task. It requires time and superhuman efforts. But we have no alternative."

Meanwhile, Russia said it was investigating the torture of its soldiers held prisoner in Ukraine and released as part of a recent swap with Kyiv.

Russia's Investigative Committee, which probes major crimes, said in a statement that it was "verifying facts of inhuman treatment of Russian soldier prisoners in Ukraine".

Ukraine claims that most freed soldiers had defended the Azovstal steelworks in Mariupol

Last week Moscow and Kyiv exchanged 144 prisoners of war each - the biggest exchange since President Vladimir Putin sent troops into Ukraine on 24 February.

The committee said Moscow's soldiers told investigators about "the violence they had suffered".

According to its statement, one of the soldiers said Ukrainian medics treated him without anaesthesia and that he was "beaten, tortured with electricity" in captivity.

The soldier allegedly said he was left without food and water for days.

Another injured Russian soldier, who had his leg amputated, said he was badly beaten and accused a Ukrainian medic of poking at his wound, the statement said.

The testimonies of the freed Russian soldiers are examples of "violations of the Geneva Convention on prisoners of war", the Investigative Committee said.