The Kremlin says Russia is still ready to honour agreements with Ukraine on a new prisoner of war exchange and on the repatriation of dead soldiers despite what it says is Kyiv's failure to so far honour its side of the bargain.

Russia accused Ukraine on Saturday of indefinitely postponing the exchanges, something Kyiv denied.

Kremlin spokesman Dmitry Peskov on Monday repeated Russian accusations against Ukraine.

"We have seen and heard a hundred different excuses, justifications and so on, but it is difficult to view them as credible," Peskov told reporters.

"The Russian side remains ready to implement the agreements reached in Istanbul."

The exchanges were agreed to during a second round of direct peace talks in Istanbul on June 2 and are meant to see a new prisoner of war swap of at least 1,200 POWs - focusing on the youngest and most severely wounded - as well as the repatriation of thousands of bodies of those killed in the war.

The return of prisoners of war and the return of the bodies of the dead is one of the few things the two sides had been able to agree on, even as their broader negotiations have failed to get close to ending the war, now in its fourth year.

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Kremlin aide Vladimir Medinsky said on Saturday that the Russian side had shown up at the agreed exchange point with the bodies of 1,212 Ukrainian dead soldiers only to find nobody from Ukraine to take them. He said a first list of 640 POWs had also been handed to Ukraine in order to begin the exchange.

Ukrainian officials rejected those accusations and President Volodymyr Zelensky vowed on Sunday to press on with prisoner exchanges despite tensions around the issue.

He said though that Ukraine had not yet received a full list of prisoners to be released and accused Moscow of "trying to play some kind of dirty political and information game."