WASHINGTON — The Trump administration notified international partners on Thursday that it’s pulling out of a treaty that permits 30-plus nations to conduct unarmed, observation flights over each other’s territory — overflights initially set up to promote trust and avert conflict between the U.S. and Russia.

The administration says it wants out of the Open Skies Treaty because Russia is violating the pact and imagery collected during the flights can be obtained quickly at less cost from U.S. or commercial satellites. Exiting the treaty, however, is expected to strain relations with Moscow and upset some members of Congress and European allies, which benefit from the imagery collected by Open Skies flights conducted by the U.S.

President Dwight Eisenhower first proposed the United States and the former Soviet Union allow aerial reconnaissance flights over each other’s territory in July 1955. At first, Moscow rejected the idea, but President George H.W. Bush revived it in May 1989, and the treaty entered into force in January 2002. Thirty-four nations have signed it; Kyrgyzstan has signed but not ratified it.

More than 1,500 flights have been conducted under the treaty, aimed at fostering transparency about military activity and helping monitor arms control and other agreements. Each nation in the treaty agrees to make all its territory available for surveillance flights and share all the imagery collected, yet Russia has restricted flights over certain areas.

Alexandra Bell, a former State Department official and currently the senior policy director at the nonpartisan nonprofit Center for Arms Control and Non-Proliferation, said withdrawal from Open Skies will rub allies the wrong way.

“I absolutely cannot see a single upside to abandoning this treaty against the advice and wishes of our allies, other than for the people who never liked this treaty and don’t like the idea of the transparency and openness the treaty provides,” Bell said.

The U.S. has been working on a proposal to share with partners and allies imagery the U.S. would have shared from its Open Skies flights, said senior administration officials, who spoke on condition of anonymity to explain Trump’s decision.

Bell noted the concept had been developed during the Eisenhower administration, advanced by President George H.W. Bush and brought into force during the administration of George W. Bush.

“It’s a Republican legacy treaty,” she said.

Sen. Tom Cotton, R-Ark., called leaving the treaty another positive step to end America's dependence on “dysfunctional and broken" treaties and said it was outdated — “irrelevant as the VHS recorder or cassette deck.”

Last month, top Democrats on the Foreign Affairs and Armed Services committees in the House and the Senate wrote to Trump accusing the president of “ramming” a withdrawal from the treaty as the world grapples with COVID-19. They said it would undermine U.S. alliances with European allies who rely on the treaty to keep Russia accountable for its military activities in the region.

“The administration’s effort to make a major change to our national security policy in the midst of a global health crisis is not only shortsighted, but also unconscionable,” wrote Reps. Adam Smith, D-Wash., and Eliot Engel, D-N.Y., and Sens. Jack Reed, D-R.I., and Bob Menendez, D-N.J.

This month, 16 former senior European military and defense officials signed a statement supporting the treaty, saying a U.S. withdrawal would be a blow to global security and further undermine the international arms control agreements.

The officials asked the U.S. to reconsider its exit. But if the U.S. leaves, they called for European states to stay in the treaty, fulfill obligations under the treaty and refrain from restricting the length of observation flights or banning flights over certain territories.

There's also concern Russia might want to pull out of the treaty. If the U.S. and Russia exit, all U.S. and Russian territory would be off limits to the overflights. That prompts arms control experts like Steve Pifer at the Brookings Institution to ask “What would be the point?'” On the other hand, he said, Moscow could opt to stay in the treaty, which would at least allow it to continue overflights of American facilities in Europe.

Trump’s decision to exit the Open Skies Treaty also raises questions about his commitment to extending or renegotiating the New START treaty, which expires early next year. The senior administration officials insist the Trump administration is committed to arms control and European security.

New START, the only remaining treaty constraining the U.S. and Russian nuclear arsenals, imposes limits on the number of U.S. and Russian long-range nuclear warheads and launchers. Russia has offered to extend the treaty, but Trump is holding out in hopes of negotiating a three-way agreement with the U.S. and China.

Last year, the Trump administration announced it was pulling the plug on the 1987 nuclear arms treaty with Russia. That treaty, signed by President Ronald Reagan and Soviet leader Mikhail Gorbachev, banned production, testing and deployment of land-based cruise and ballistic missiles with a range of 500 to 5,500 kilometers (310 to 3,410 miles).

Senior administration officials said Trump last fall ordered a comprehensive review of the costs and benefits of U.S. participation in the Open Skies Treaty. At the end of an eight-month review, it became clear it was no longer in America’s interest to remain party to the treaty, the officials said. The U.S. will formally pull out in six months.

The senior administration officials said Russian violations of the treaty were the main reason for exiting. They said Russia has restricted flights over Moscow and Chechnya and near Abkhazia and South Ossetia. Russian restrictions also make it difficult to conduct observation in the Kaliningrad, a Russian enclave sandwiched between Lithuania and Poland that is home to Russia’s Baltic fleet, they said.

Russia uses illegal overflight restrictions along the Georgian border in support of its propaganda narrative that the Russian-occupied enclaves of Georgia are independent countries. The senior administration officials said that amounted to an illegal restriction, under the treaty, coupled with a narrative that justifies Russia’s regional aggression.

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Associated Press writers Matthew Lee and Robert Burns contributed to this report.