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.

Ukraine and Western governments want Russia to agree to an immediate, unconditional ceasefire lasting at least 30 days, but a Ukrainian source said Russia's demands were too much.

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.