U.S. President Donald Trump's offer to join proposed Ukraine-Russia peace talks triggered a flurry of diplomacy as powers from Europe to the Middle East sought a possible path out of the deadliest conflict in Europe since World War Two.

Russian President Vladimir Putin on Sunday proposed direct talks with Ukraine and, after Trump publicly told Ukrainian President Volodymyr Zelenskyy to accept, Zelenskyy said he would but that Putin should attend in person.

Then in a surprise on Monday, Trump — who is due to visit Saudi Arabia, the United Arab Emirates and Qatar this week, offered to join the Ukraine-Russia talks in the Turkish city of Istanbul, which straddles the divide between Europe and Asia.