After dangling the possibility of his attendance, Trump said he would stay away but still wants to meet with Putin, further weakening the Istanbul talks.

Ten days of intense diplomatic maneuvers by Europeans and the US ahead of the meeting in Turkey were insufficient to reach a deal, as the differences between the two belligerent parties appear insurmountable.

Ukraine will make securing a ceasefire a priority in expected talks with a Russian delegation in Istanbul on Friday, a Ukrainian diplomatic source said, adding there was also a need for "confidence-building measures".