Russia said it had started the process of withdrawing from the Open Skies treaty in response to the U.S. move in November to pull out of the agreement.

The Foreign Ministry said the outgoing U.S. administration’s decision to end its participation in the accord removed a key “instrument to strengthen trust and security,” according to a website statement on Friday. It also blamed U.S. allies in Europe for failing to take the steps needed to preserve the treaty after Washington’s pullout.

The treaty, which was signed in 1992 and came into force in 2002, allows countries to fly over each other’s territory for unarmed reconnaissance flights. It was intended by its almost three dozen ratifiers to reduce the risk of war.

Trump officials accused Russia of non-compliance, a charge Moscow denied. The pullout was criticized by a top Democrat, who urged President-elect Joe Biden to reverse the move.