Ten European Union countries have expressed regret at US plans to withdraw from the Open Skies Treaty, as NATO envoys met to discuss developments.
US President Donald Trump said Russian violations make it untenable for the US to remain in the arms control pact, which allows observation flights over more than 30 nations.
Washington has signalled it will pull out in six months, but a joint statement from the European nations valued the military transparency brought about by the treaty.
European nations have conducted most of the flights, often above Russia and Belarus.
The foreign ministries of Belgium, the Czech Republic, Finland, France, Germany, Italy, Luxembourg, the Netherlands, Spain and Sweden said the pact was “functioning and useful".
They also shared US concerns over Russia's implementation of the deal.
"The Open Skies Treaty 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," the statement said.
"We will continue to implement the Open Skies Treaty, which has a clear added value for our conventional arms control architecture and cooperative security.
"Regarding issues on Treaty implementation, we will continue to engage Russia...to address outstanding issues such as the undue restrictions to flights over Kaliningrad.
"We continue to call on the Russian Federation to lift these restrictions and continue our dialogue with all parties."
In 2018, NATO leaders expressed concern about “Russia’s ongoing selective implementation” of the treaty and other conventional arms control pacts.
German foreign minister Heiko Maas earlier said Russian foul play under the treaty "does not justify" a US pullout.
Mr Trump has left the door open for Russian renegotiation.
Last year, Mr Trump withdrew the US from the Intermediate-Range Nuclear Forces treaty that it agreed in 1987 with the Soviet Union, blaming Moscow for developing a missile that did not comply with it.
Cover image: US military personnel walking away from an Open Skies aircraft with surveillance photography (Picture: US Department of Defense).