Recep Tayyip Erdogan, the president of Turkey, rejected a US demand that he halt the Turkish offensive in northern Syria but is expected to fly to Moscow to talk about the crisis with Vladimir Putin.

Donald Trump has dispatched Mike Pence and Mike Pompeo, the US secretary of state, to Ankara in a bid to calm the greatest crisis between the US and a Nato ally in living memory.

Mr Pence said he would meet with Mr Erdogan on Thursday and "voice the United States' commitment to reach an immediate ceasefire and the conditions for a negotiated settlement."

He reiterated that Mr Trump will pursue "punishing economic sanctions" until a resolution is reached.

But Mr Erdogan said on Wednesday that he would only halt the offensive if Kurdish-led forces quit a designated border area "by tonight."

"There are some leaders who are trying to mediate... There has never been any such thing in the history of the Turkish republic as the state sitting at the same table with a terror organisation," he said in an address to the Turkish parliament.