Ukraine has unexpectedly postponed exchanging prisoners of war and accepting the bodies of killed soldiers for an indefinite period, Kremlin aide Vladimir Medinsky said on Saturday.Russia and Ukraine held the second round of peace talks in Istanbul on Monday where they agreed to exchange more prisoners - focusing on the youngest and most severely wounded - and to return the bodies of 12,

Russia and Ukraine wrangled over details of a large prisoner swap, with officials in Kyiv rejecting claims by a Russian negotiator that they were dragging their feet on the planned exchange.

A large-scale prisoner exchange between Russia and Ukraine -- the only concrete outcome of peace talks -- was thrown into doubt Saturday after Moscow and Kyiv accused each other of delaying and thwarting the swap.