U.S. Secretary of State Marco Rubio will not attend crunch talks on a ceasefire for Ukraine in London on Wednesday, after Ukrainian President Volodymyr Zelensky doubled down on a refusal to recognize Russian control over Crimea as part of a future agreement.

Diplomats from the UK, France, Germany, Ukraine and the US will hold fresh talks in London on Wednesday aimed at securing a ceasefire in the three-year war between Ukraine and Russia. The talks come amid growing speculation that Russia might be willing to halt its invasion along current front lines in return for significant concessions.

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.