Former President Donald Trump criticized Ukrainian President Volodymyr Zelenskyy for rejecting peace talks over Russia’s annexation of Crimea, calling Zelenskyy’s stance “very harmful” to ending the war.

Trump said negotiations with Zelenskyy have been tougher than with Putin and paused U.S. military aid after a heated Oval Office clash.

Zelenskyy maintains that giving up Crimea violates Ukraine’s constitution.

Peace efforts have faltered, with U.S. officials pulling out of talks in London, although some progress was reported in follow-up meetings, NBC News has reported.

Ukraine and the U.S. remain far apart on terms, especially regarding Crimea.

Written by B.C. Begley