Russian President Vladimir Putin said on Tuesday that residents of separatist-held regions of eastern Ukraine could be targeted by government forces if Kiev is granted total control over the border between them and Russia.

Speaking a day after his first face-to-face meeting with Ukrainian President Volodymyr Zelenskiy, Putin evoked the memory of the 1995 Srebrenica massacre during the Bosnia war.

He said an amnesty for residents of Donetsk and Luhansk must be granted prior to any handover.

"The amnesty law still hasn't been passed. While the Ukrainian side keeps insisting: 'give us the opportunity to close the border using our troops'. But I can imagine what would happen next," Putin said.

"There would be Srebrenica, as simple as that," Putin said, referring to the massacre in which Bosnian Serbs killed more than 8,000 Muslims — the worst mass slaughter on European soil since World War Two.

The conflict in eastern Ukraine, pitting Moscow-backed rebels against the Ukraine government, has killed more than 13,000 people and aggravated the deepest east-west rift since the Cold War.

During their meeting in Paris on Monday, Putin and Zelenskiy agreed to exchange all remaining prisoners from the conflict, but many questions about the region's future status remain up in the air.