The chairman of the House Foreign Affairs Committee has expressed alarm that the US is thought to be considering pulling out of a vital treaty with European allies and Russia.

In a letter sent to the US national security adviser on Monday, Rep. Eliot Engel of New York said he was "deeply concerned" by reports that the White House was considering withdrawing from the Open Skies Treaty.

Under Open Skies, countries that are part of the treaty must notify other nations 72 hours in advance of a mission to conduct an observational flight, to which the host country has one day to respond.

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The chairman of the House Foreign Affairs Committee has expressed alarm with the possibility that the US will pull out of a vital treaty with European allies and Russia.

Rep. Eliot Engel of New York on Monday sent a letter to the US national security adviser, Robert O'Brien, in which he said he was "deeply concerned" by reports that the White House was considering withdrawing from the Open Skies Treaty.

"I request your personal engagement on this matter to ensure that the United States does not unwisely and rashly withdraw from the Open Skies Treaty, which continues to serve American national security interests and is particularly important as a check against further Russian aggression against Ukraine," Engel wrote.

The Open Skies Treaty was signed by the US, Russia, and 22 other countries in an effort to promote transparency among nations. Thirty-four countries are now members of the treaty, which was initially signed in 1992.

Countries that are part of the treaty must notify other nations 72 hours in advance of missions to conduct an observational flight, to which the host country has one day to respond.

Daryl Kimball, the executive director of the Arms Control Association, agrees that the treaty has been beneficial for the US, its allies, and even Russia.

"The treaty provides information about Russian military activities for the US and allies in Europe," Kimball told Business Insider. "And it also provides the Russians with some insight about some of our capabilities. And that transparency reduces uncertainty and the risk of conflict due to worst-case assumptions."

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Earlier this year, a Russian Tu-154 aircraft conducted an observational mission over Great Falls, Montana, and took aerial photographs for several days.

"This is not a spying operation," Kimball said. "These are observational flights. It is a form of monitoring and verification about the military activities and facilities on each side."

Kimball said the US had significant satellite capabilities that could mitigate a lapse in observational flights, but he added that a pullout from the treaty might affect US allies.

"Where this is particularly valuable is for our allies who don't have these capabilities," Kimball said. "We should not dispense with this treaty that's been working for a couple of decades now."

There has been tension between the US and Russia over claims from both countries that the other is violating the treaty.

In 2018, Russian officials accused the US of violating the spirit of the agreement by not approving its aircraft to conduct observational missions, according to Defense News. Russian media outlets also reportedly said the US had withdrawn from the treaty, which US officials denied.

The US in turn has also accused Russia of restricting its flight access. US officials previously accused Russia of violating the treaty by restricting flights in Kaliningrad, a heavily militarized area that is home to short-range missiles. In response to Russia's denial, Republican Sen. Tom Cotton of Arkansas characterized the outrage as hypocrisy and advocated a US withdrawal from the treaty.

"It's rich for the Russians to protest the US's refusal to certify one of their planes for the Open Skies Treaty when they routinely restrict surveillance flights over Kaliningrad," Cotton said in a tweet. "The Open Skies Treaty is out of date and favors Russia, and the best way forward is to leave it."

Despite the impasse, Engel said the US should not haphazardly withdraw from the treaty. "US relations with Russia have become more acrimonious and complicated in the last decade," he said in his letter. "The United States should prepare for the challenge that Russia presents — not abandon mechanisms that provide the United States with an important tool in maintaining surveillance on Russia."

Kimball agreed and said there were still strategic benefits for the US to uphold its commitment to the treaty.

"I don't see any practical value in pulling out," Kimball said. "It doesn't gain any capability that we are being denied, it doesn't deny the Russians information that they can't otherwise obtain through their own satellites. This is a confidence-building treaty that is particularly valuable to our European allies and particularly in a time of increasing US-Russian tensions."

The US State Department and the National Security Council did not respond to requests for comment.