Russia is likely concentrating equipment on the front line in the direction of Siversk, about 8 km (4.9 miles) west of the current Russian front line, Britain's defense ministry said on Friday.
Russian forces are likely pausing to replenish before undertaking new offensive operations in the Donetsk Oblast, the Ministry of Defence said in a Twitter update.
The ministry said that there is a realistic possibility that Russia's immediate tactical objective will be Siversk, as its forces attempt to advance towards its most likely operational goal of the Sloviansk-Kramatorsk urban area.
The Federation Council, the upper chamber of Russia's parliament, on Friday barred British diplomats, including the ambassador, from accessing its building, Russian news agencies reported.
Snake Island is a warning to Russia: Ukraine 'will not be broken'
President Volodymyr Zelensky said the raising of the Ukrainian flag on Snake Island in the Black Sea was a sign his country would not be broken, as President Vladimir Putin warned the West that its efforts to defeat him would bring tragedy to Ukraine.
"Let every Russian captain, aboard a ship or a plane, see the Ukrainian flag on Snake Island and let him know that our country will not be broken,"Ukrainian President Volodymyr Zelensky
In a hawkish speech to parliamentary leaders more than four months into the war, Putin said Russia had barely got started in Ukraine and the prospects for negotiation would grow dimmer the longer the conflict dragged on.
"We have heard many times that the West wants to fight us to the last Ukrainian. This is a tragedy for the Ukrainian people, but it seems that everything is heading towards this," he said.
Zelensky, in his nightly video message on Thursday, responded with defiance, saying that the two-month operation to retake Snake Island was a warning to all Russian forces.
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"Let every Russian captain, aboard a ship or a plane, see the Ukrainian flag on Snake Island and let him know that our country will not be broken," he said.
Snake Island, a speck south of the port of Odesa, has become a symbol of Ukrainian determination.
In February, when ordered to surrender the small Ukrainian garrison on the island swore at their Russian attackers and were hit by an air strike.
Russia abandoned the island at the end of June in what it said was a gesture of goodwill - a victory for Ukraine that Kyiv hoped could loosen Moscow's blockade of Ukrainian ports.
On Thursday Ukraine's raised its blue-and-yellow flag on its recaptured Snake Island. Moscow responded with its warplanes striking the island and destroying part of the Ukrainian detachment there, it said.
Putin invaded Ukraine on Feb. 24, in what he called a "special military operation" to demilitarize Ukraine, root out dangerous nationalists and protect Russian speakers. Ukraine and its allies say Russia launched an imperial-style land grab.
The biggest conflict in Europe since World War II has killed thousands, displaced millions and flattened scores of Ukrainian cities. Kyiv and the West accuse Russian forces of war crimes, but Moscow says it does not target civilians.
Ukraine loses Johnson
On Thursday, Kyiv lost one of its main international supporters after British Prime Minister Boris Johnson said he would step down. Moscow did not conceal its delight at the political demise of a leader whom it has long criticized for arming Kyiv so energetically.
In a phone call, Johnson told Ukraine's President Volodymyr Zelensky "You're a hero, everybody loves you," a spokesman for Johnson said.
"Britain's support for Ukraine will not change whatever happens in the corridors of power in London. Boris and all our friends in the United Kingdom have assured us of that," Zelensky said in his nightly video address.
Johnson's resignation comes at a time of domestic turmoil in some other European countries that support Kyiv and doubts about their staying power for what has become a protracted conflict.
After failing to quickly take the capital Kyiv, Russia is now engaged in a war of attrition in Ukraine's eastern, industrial heartland of the Donbas.
On Sunday, Moscow declared it had "liberated" the Luhansk region and now plans to capture parts of neighboring Donetsk it does not control. Luhansk and Donetsk make up the Donbas.
The mayor of the Donetsk city of Kramatorsk said Russian forces had fired missiles at the city center in an air strike on Thursday and that at least one person was killed and six wounded.
Pavlo Kyrylenko, governor of the Donetsk region, said the missile had damaged six buildings including a hotel and an apartment bloc in the large industrial hub.
Reuters could not independently verify those assertions.
Losses and casualties
In Kramatorsk, mechanic-turned-soldier Artchk helped shore up defenses against imminent Russian attack while, nearby, farmer Vasyl Avramenko lamented the loss of crops supplanted by mines.
"Of course we're already prepared. We're ready," Artchk, identifying himself by his nom-de-guerre, told Reuters.
"It's their (Russians') fantasy to occupy these cities, but they don't expect the level of resistance. It's not just the Ukrainian government, it's the people who refuse to accept them."
The regional governor of the northeastern city of Kharkiv said late on Thursday that three people had been killed and another five wounded after Russian forces shelled the city.
In the aftermath, bodies lying on the ground near a park bench were covered in sheets by emergency services. Two women who had gone out to feed cats in the area had been killed, said local resident Yurii Chernomorets.
A man fell to his knees weeping as the bloodied corpse of his wife was placed in a body bag. He kissed her hand.
"Dad, she is dead, please get up," said a man who identified himself as their son.