Updated May 22, 2020, at 12:24 p.m. EST with comments from NATO and Poland.

BRUSSELS — Ten European Union countries on Friday expressed regret at U.S. plans to withdraw from the Open Skies treaty and vowed to uphold the pact, as NATO envoys met to discuss developments.

President Donald Trump said Thursday that Russian violations make it untenable for the United States to stay in the Open Skies Treaty. Washington has signaled that it will pull out in six months, although Trump hinted that he might reconsider the decision.

The treaty came into force in 2002. It was meant to promote trust between the U.S. and Russia by allowing signatories to conduct reconnaissance flights over each other’s territories to collect information about military forces and activities.

In a joint statement, the foreign ministries of Belgium, the Czech Republic, Finland, France, Germany, Italy, Luxembourg, the Netherlands, Spain and Sweden said the pact “is a crucial element of the confidence-building framework that was created over the past decades in order to improve transparency and security across the Euro-Atlantic area.”

“We will continue to implement the Open Skies Treaty, which has a clear added value for our conventional arms control architecture and cooperative security. We reaffirm that this treaty remains functioning and useful,” the 10 EU members said, even though they share U.S. concerns about Russia’s respect of the pact.

They called on Russia to lift flight restrictions, notably over its Kaliningrad region, which lies between NATO allies Lithuania and Poland. Of the 10 countries, Finland and Sweden are not NATO members. Sweden has been particularly active in trying to save the treaty over the last six months.

Poland also issued an individual statement, saying the U.S. has “been keeping the Republic of Poland informed about the Treaty on Open Skies’ implementation review and its possible decision on withdrawal. We are currently taking actions together with our Allies and close partners to agree on joint solutions aimed at strengthening our security.”

After several hours of meetings, NATO Secretary General Jens Stoltenberg issued the alliance’s comment on the situation, saying the allies “agree that all states party to the Open Skies Treaty must fully implement their commitments and obligations. All NATO Allies are in full compliance with all provisions of the Treaty.”

“Russia’s ongoing selective implementation has undermined the Open Skies Treaty,” Stoltenberg added. “NATO Allies are engaging with Russia to seek Russia’s return to compliance at the earliest date possible."

Although not all NATO members are part of the treaty, the alliance often serves as a venue for coordination around multinational security arrangements. In 2018, NATO leaders expressed concern about “Russia’s ongoing selective implementation” of the treaty and other conventional arms control pacts. European nations have conducted most of the flights, which often take place over Russia and Belarus.

Earlier, German Foreign Minister Heiko Maas acknowledged that Russia was not respecting the treaty, “but from our point of view, this does not justify a withdrawal.” He said his counterparts in Britain, France and Poland have repeatedly made this clear to Washington, and that Germany “will work intensively in this time with our like-minded partners for the U.S. to reconsider its decision.”

Last year, Trump pulled the U.S. — by far the biggest and most influential of the 30 NATO member countries — out of the Intermediate-Range Nuclear Forces Treaty that it agreed in 1987 with the Soviet Union, blaming Moscow for developing a missile that does not comply with it.

Russian Deputy Foreign Minister Alexander Grushko has criticized the latest U.S. move.

“The withdrawal of the U.S. from this treaty will come as yet another blow to the system of military security in Europe, which is already weakened by the previous moves by the administration,” Grushko told Russian state news agency Tass.

It is unclear what Russia will do going forward, with one European source telling Defense News that Moscow now has the upper hand from a public relations perspective.

“If you’re Russia, you can stay in and take the moral high ground, say, ‘We still honor international treaties, even if America doesn’t,’ or you can say the treaty is diminished beyond usefulness and you pull out. I don’t know which they’ll do, but neither is good for NATO," the source said.

Geir Moulson in Berlin contributed to this report.