A new meeting is expected next week in London, and Rubio suggested that could be decisive in determining whether the Trump administration continues its involvement.

The Trump administration made clear it will abandon peace attempts for Ukraine if Russia fails to adhere to any terms, but the president did not say whether there would be consequences.

Washington is ready to cease its mediation efforts to end Russia's war against Ukraine if one of the sides "makes it very difficult" to settle, U.S. President Donald Trump told journalists on April 18.