By Tom Balmforth

CHERNIHIV REGION, Ukraine (Reuters) -Russia and Ukraine each released 390 prisoners on Friday and said they would free more in the coming days, in what is expected to be the biggest prisoner swap of the war so far.

The agreement to exchange 1,000 prisoners each was the only concrete step towards peace to emerge last week from two hours of talks in Istanbul, the first direct talks between the warring sides in more than three years.

They failed to agree to a ceasefire proposed by U.S. President Donald Trump.

The Russian ministry of defence said each side had released 270 soldiers and 120 civilians on Friday. Ukrainian President Volodymyr Zelenskiy confirmed the total of 390 each, and said more would be released on Saturday and Sunday.

Earlier, Ukrainian authorities told reporters to assemble at a location in the northern Chernihiv region in anticipation that some freed prisoners could be brought there.

Referring to the prisoner swap earlier on Friday, Trump wrote on Truth Social: "Congratulations to both sides on this negotiation. This could lead to something big???"

Hundreds of thousands of soldiers on both sides are believed to have been wounded or killed in Europe's deadliest war since World War Two, although neither side publishes accurate casualty figures. Tens of thousands of Ukrainian civilians have also died as Russian forces have besieged and bombarded Ukrainian cities.

The Russian defence ministry said those released included civilians captured in Russia's Kursk region during a Ukrainian incursion there that began last year.

The freed Russian servicemen and civilians were in Belarus, which neighbours Ukraine, and receiving psychological and medical assistance before being moved to Russia for further care, it said.

CEASEFIRE?

Ukraine says it is ready for a 30-day ceasefire immediately.

Russia, which launched the war by invading its neighbour in 2022 and now occupies about a fifth of Ukraine, says it will not pause its assaults until conditions are met first. A member of the Ukrainian delegation called those conditions "non-starters".

Trump, who has shifted U.S. policy from supporting Ukraine towards accepting some of Russia's account of the war, had said he could tighten sanctions on Moscow if it blocked peace. But after speaking to Putin on Monday he decided to take no action for now.

Moscow says it is ready for talks while the fighting goes on, and wants to discuss what it calls the war's "root causes", including its demands Ukraine cede more territory, and be disarmed and barred from military alliances with the West. Kyiv says that is tantamount to surrender and would leave it defenceless in the face of future Russian attacks.

Meanwhile, fighting has continued.

Russia claimed on Friday to have captured a settlement called Rakivka in Ukraine's northeastern Kharkiv region.

The governor of Ukraine's Odesa region, Oleh Kiper, said Russia had struck port infrastructure there with two missiles on Friday afternoon, killing one person and wounding eight.

(Reporting by Tom Balmforth and Abinaya Vijayaraghavan; Writing by Peter Graff; Editing by Alex Richardson and Timothy Heritage)