ISTANBUL (REUTERS) - Russian and Ukrainian negotiators began talks in Istanbul on Tuesday (March 29), and Turkish President Recep Tayyip Erdogan told them that progress would pave the way for a meeting of the countries' two leaders since the time had come for concrete results.

In a televised speech to the negotiators ahead of their first discussions in more than two weeks, Mr Erdogan called for an immediate ceasefire in the war that began last month when Russia invaded Ukraine.

"It is up to the sides to stop this tragedy. Achieving a ceasefire and peace as soon as possible is to the benefit of everyone. We think we have now entered a period where concrete results are needed from talks," he said.

"The negotiating process, which you have been carrying out under the orders of your leaders, has raised hopes for peace."

The Ukrainian embassy in Ankara said the delegation heads had begun talks and discussions would follow between the full delegations.

Foreign Minister Dmytro Kuleba said on Monday that Ukraine's most ambitious goal at the Turkey talks this week was to agree a ceasefire.

A senior US official said Russian President Vladimir Putin does not appear ready to make compromises to end the war.

North Atlantic Treaty Organisation member Turkey shares a maritime border with Ukraine and Russia in the Black Sea, has good ties with both and has offered to mediate the conflict.

While calling Moscow's invasion unacceptable, Ankara has also opposed the Western sanctions.