Russian forces pounded areas around Kyiv and another Ukrainian city overnight, local officials said, hours after Moscow pledged to scale back military operations in those places.

The shelling further tempered optimism about possible progress in talks in Turkey aimed at ending the punishing war.

Moscow did not spell out what exactly a reduction in activity would look like, and while the promise initially raised hopes that a path towards ending the bloody war of attrition was at hand, Ukraine’s president and others cautioned that the commitments could merely be bluster.

Russia reacted coolly on Wednesday to Kyiv’s proposed framework for a peace deal, with Kremlin spokesman Dmitry Peskov saying it was a “positive factor” that Ukraine has submitted its written proposals but added that he saw no breakthrough.

The UK Ministry of Defence said heavy losses have forced some Russian units to return to Belarus and Russia to regroup, but that Moscow was likely to compensate for any reduction in ground manoeuvres by using mass artillery and missile barrages.

The Russian military reported a new series of missile strikes on Ukrainian arsenals and fuel depots over the past 24 hours.

The United Nations said the number of refugees fleeing the country has passed four million, while Poland announced steps to end all Russian oil imports by the end of the year, and Germany issued a warning over its natural gas supplies amid concerns that Russia could cut off deliveries unless it is paid in roubles.

Ukrainian President Volodymyr Zelensky reacted with scepticism to Russia’s announcement at talks in Istanbul on Tuesday that it would reduce military activity near the capital and the northern city of Chernihiv.

“We can call those signals that we hear at the negotiations positive,” he said in his nightly video address to the Ukrainian people. “But those signals don’t silence the explosions of Russian shells.”

“The so-called reduction of activity in the Chernihiv region was demonstrated by the enemy strikes including air strikes on Nizhyn, and all night long they were shelling Chernihiv,” said regional governor Viacheslav Chaus.

“Civilian infrastructure facilities, libraries, shopping centres, many houses were destroyed in Chernihiv.”

Oleksandr Pavliuk, head of the Kyiv region military administration, said Russian shells had targeted residential areas and civilian infrastructure in the Bucha, Brovary and Vyshhorod regions around the capital.

Russian Defence Ministry spokesman Major General Igor Konashenkov said the military targeted fuel depots in two towns in central Ukraine with air-launched long-range cruise missiles.

Russian forces also hit a Ukrainian special forces headquarters in the southern Mykolaiv region, he said, and two ammunition depots in eastern Donetsk.

Donetsk is in the eastern industrial heartland of Donbas, where the Russian military says it has shifted its focus. Senior Russian military officials have said twice in recent days that their main goal now is the “liberation” of Donbas, where Moscow-backed rebels have been battling Ukrainian forces since 2014.

Some analysts have suggested the Kremlin’s apparent lowering of its aims and the pledge to reduce activity around Kyiv and Chernihiv may merely reflect the reality on the ground, as ground troops have become bogged down and taken heavy losses in their bid to seize the capital and other cities.

Ukraine’s delegation in Istanbul offered a detailed framework for a peace deal under which a neutral Ukraine’s security would be guaranteed by a group of third countries, including the US, Britain, France, Turkey, China and Poland. Among other items, the Kremlin has demanded all along that Ukraine drop any hope of joining Nato.

Russian delegation head Vladimir Medinsky said negotiators would take the Ukrainian framework to President Vladimir Putin and Moscow would provide a response, but he did not say when.

Deputy defence minister Alexander Fomin said Moscow would in the meantime “fundamentally… cut back military activity in the direction of Kyiv and Chernihiv” to “increase mutual trust and create conditions for further negotiations”.

The talks had been expected to resume on Wednesday, but with what Turkish foreign minister Mevlut Cavusoglu called “meaningful” progress, the two sides decided to return home for consultations.

Mr Zelensky warned the world and his own people not to get ahead of themselves.

“Ukrainians are not naïve people,” he said. “Ukrainians have already learned during the 34 days of the invasion and during the past eight years of war in the Donbas that you can trust only concrete results.”

Western countries also expressed doubts about Russia’s intentions.

An assessment from the MoD said Russia’s focus on the Donbas region “is likely a tacit admission that it is struggling to sustain more than one significant axis of advance”.

“Russian units suffering heavy losses have been forced to return to Belarus and Russia to reorganise and resupply,” the ministry said in a statement.

“Such activity is placing further pressure on Russia’s already strained logistics and demonstrates the difficulties Russia is having reorganising its units in forward areas within Ukraine.”

Pentagon spokesman John Kirby said the US had detected small numbers of Russian ground forces moving away from the Kyiv area, but it appeared to be a repositioning of forces, “not a real withdrawal”.

US President Joe Biden and his secretary of state, Antony Blinken, said they would wait to see what Russia’s actions are.

Even as negotiators gathered on Tuesday, Russia’s deadly siege in the south continued, with civilians trapped in the ruins of Mariupol and other devastated cities, while Mr Putin’s forces blasted a gaping hole in a nine-storey government building in the port city of Mykolaiv, killing at least 14 people, emergency authorities said.