Doubts about today's talks: What do we know?

Talks in Istanbul between Ukrainian, Russian and US delegations had been scheduled for 10:00 local time (08:00 BST) in Istanbul's Dolmabahce Palace.

Russia's foreign ministry spokeswoman, Maria Zakharova, says the talks have been postponed until later today, at Turkey's behest.

Russia's delegation, headed by presidential aide Vladimir Medinsky, have arrived.

But, sources in Turkey's foreign ministry tell the BBC "there is no scheduled meeting yet". We're told they will provide an update if, or when, plans for a meeting are finalised.

They confirm that a Russian delegation and some US officials have arrived in Istanbul, as US Secretary of State Marco Rubio is meeting Nato foreign ministers in Antalya.

Meanwhile Ukrainian President Zelensky has landed in Ankara in the past hour ahead of meeting Turkish President Recep Tayyip Erdogan.

We're waiting for more certainty on when Ukraine-Russia talks in Istanbul will happen, and we'll bring you the key developments as we get them. Stay with us.