Talks between the U.S., Ukraine and European officials to discuss ending Russia's war in Ukraine faltered as Secretary of State Marco Rubio abruptly cancelled his trip to London.

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.

In meetings this month in Paris and London and in exchanges via allied channels, U.S. and Ukrainian officials, including Marco Rubio, have discussed possible terms of a negotiated settlement involving Russia and traded proposals and counterproposals.