A planned meeting Wednesday between top U.S., British, French and Ukrainian diplomats to push forward a peace deal between Russia and Ukraine was scrapped at the last minute, with U.S. Vice President JD Vance saying negotiations are reaching a moment of truth.

U.S. Secretary of State Marco Rubio will not attend talks in London aimed at ending the war in Ukraine, State Department spokesperson Tammy Bruce said on Tuesday, after earlier saying he planned to travel to London.

A major meeting in London aimed at bringing about an end to Russia’s war in Ukraine has been downgraded after US Secretary of State Marco Rubio said he would skip the summit, escalating a clash between Washington and Kyiv over the future of Russian-occupied Crimea.