Russia has handed over to Ukraine the bodies of 1,000 soldiers as part of an agreement reached at peace talks last month in Istanbul, Moscow's top negotiator said on social media.

Two rounds of negotiations in Istanbul between Moscow and Kiev have yet to produce a ceasefire agreement, but have nonetheless led to large-scale prisoner exchanges and deals to return the bodies of killed soldiers.

"Following the agreements reached in Istanbul, another 1,000 bodies of Ukrainian soldiers were handed over to Ukraine today," Russian negotiator and Kremlin aide Vladimir Medinsky said Thursday on Telegram.

Ukraine handed over 19 killed Russian soldiers, he added.

He posted photos showing people in white medical suits lifting white body bags from the back of refrigerated trucks.

Exchanges of captured soldiers and the repatriation of remains have taken place regularly throughout the conflict, in some of the only successful diplomacy between the sides.

At the talks last month, Russia outlined a list of demands, including for Ukraine to cede more territory and to reject all forms of Western military support.

Kiev dismissed them as unacceptable ultimatums and has questioned the point of further negotiations if Moscow is not willing to make concessions.