Turkish President Tayyip Erdogan welcomed delegations from both sides saying that "stopping this tragedy" was up to them.

Ukrainian television reported the talks had begun with "a cold welcome" and no handshake between the delegations.

Ukraine and the United States hold little hope of an immediate breakthrough. But the resumption of face-to-face talks is an important first step towards a ceasefire in a Russian invasion that is stalled on most fronts but inflicting horrible suffering on civilians trapped in besieged cities.

More than a month into the war, the biggest attack on a European nation since World War Two, more than 3.8 million people have fled abroad, thousands have been killed and injured, and Russia's economy has been pummelled by sanctions.

In the besieged southern port city of Mariupol nearly 5,000 people have been killed, including about 210 children, according to figures from the mayor. Such figures cannot be verified.

Survivors have told harrowing tales of people dying from lack of medical treatment, bodies being buried wherever space could be found, and women giving birth in basements.

Ukrainian Foreign Minister Dmytro Kuleba said of the talks in Turkey: "We are not trading people, land or sovereignty."

"The minimum programme will be humanitarian questions, and the maximum programme is reaching an agreement on a ceasefire," he said on national television.

A senior U.S. State Department official said Russian President Vladimir Putin did not appear ready to make compromises to end the war. 

Kremlin spokesperson Dmitry Peskov said talks so far had not yielded any substantial progress but it was important they continued in person.