The Kremlin says it is concerned about U.S. President Donald Trump’s decision to withdraw from a landmark nuclear weapons treaty.

Trump announced on Saturday that the United States would walk away from the Intermediate-Range Nuclear Forces Treaty that the U.S. and the Soviet Union signed in 1987 in a major step to ease Cold War tensions.

Dmitry Peskov, spokesman for Russian President Vladimir Putin, told reporters Putin is denying Trump’s allegations that Russia has violated terms of the treaty. Peskov says the U.S. withdrawal from the treaty would “make the world a more dangerous place.”

The Kremlin’s comments came as U.S. National Security Adviser John Bolton began his visit to Russia today. Peskov said Russian officials are anxious to hear Bolton’s explanations for Trump’s decision.