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 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".

Russia and Ukraine held their first direct peace talks in three years in Istanbul, but deep divisions and ongoing conflict tempered hopes for immediate progress toward ending the war.