WASHINGTON — Four senior Democratic lawmakers said on Tuesday they believed the Trump administration may withdraw from a treaty that allows unarmed surveillance flights over U.S., Russian and other territory, warning it would be a gift to Russia and undermine confidence in the U.S. commitment to Ukraine.

"Pulling out of the Open Skies Treaty, an important multilateral arms control agreement, would be yet another gift from the Trump administration to (Russian President Vladimir) Putin," the Democrats on the House and Senate foreign relations and armed services committees wrote in a letter to the U.S. secretaries of state and defense seen by Reuters.

"The Open Skies Treaty is a critical element of U.S and European security, and a decision to withdraw would be another blow to regional stability as well as Ukrainian security," wrote Senators Robert Menendez and Jack Reed, respectively the top Democrats on the Senate foreign relations and armed services panels, and Congressmen Eliot Engel and Adam Smith, chairs of the House foreign affairs and armed services panels, respectively.

The treaty, which was signed in 1992 and entered into force in 2002, permits each of the nations that are parties to it to carry out short-notice, unarmed surveillance flights over the entire territory of the other parties.

The purpose of the treaty, which allows nations to collect information on each other's military forces, is to increase transparency and to build confidence among the states that are party to it, including the United States, Russia and Ukraine.

The State Department and the Pentagon did not immediately reply to a request for comment.

But in their letter, the four Democrats said the United States carried out an extraordinary flight under the treaty in December 2018, after Russia had opened fire on and seized three Ukrainian navy ships and their crews in Nov. 25 incident in the Black Sea, as well as in 2014, after Russia annexed Crimea from Ukraine.

"Withdrawing from the Open Skies Treaty would be perceived as casting further doubt on the status of the United States commitment to Ukraine's security and would advance the Russian narrative that the United States is an unreliable partner in the region," added the letter to Secretary of State Mike Pompeo and Secretary of Defense Mark Esper.