Russia is trying to undermine peace talks and should be slammed with tough new sanctions, Ukrainian President Volodymyr Zelenskyy said Thursday ahead of negotiations between the U.S. and Moscow. Ukraine agreed to a Trump administration proposal for a 30-day pause in fighting earlier this week after high-level talks with a U.

The president framed his threat as part of his effort to forge a cease-fire and permanent peace deal in Ukraine. He later defended Russia’s overnight attacks on Ukraine.

U.S. President Donald Trump raised the prospect of imposing large-scale U.S. sanctions on Russia on Friday, days after pausing military aid and intelligence support to Ukraine, and he called on both countries to get on with negotiating a peace deal.