The United States has announced it is pulling out of the Open Skies surveillance treaty, sparking UN concerns of a "dangerous new arms race".
The US has told more than 30 member nations it is leaving the treaty which allows partners to conduct unarmed, observation flights over each other's territory.
It was set up decades ago to promote trust and avoid conflict.
The US administration said it was exiting the treaty in six months' time because Russia is violating the rules.
Washington also said imagery collected during the flights can be obtained quickly and at less cost from US or commercial satellites.
Each nation in the treaty agrees to make all its territory available for surveillance flights, yet Russia has restricted flights over certain areas.
US President Donald Trump said: "Russia didn't adhere to the treaty.
"So until they adhere, we will pull out, but there’s a very good chance we’ll make a new agreement or do something to put that agreement back together.
"So I think what’s going to happen is we’re going to pull out and they (the Russians) are going to come back and want to make a deal. I think something very positive will work.”
Since 2002, more than 1,500 flights have been conducted under the agreement, aimed at improving transparency over military activity and greater arms control.
However, America's pending withdrawal has also prompted fears of further worsening US-Russia relations.
United Nations spokesman Stephane Dujarric said: "Ending such agreements without anything to replace them could result in destabilising activities such as a dangerous new arms race leading to possible miscalculations."
Political opposition have criticised Mr Trump for the withdrawal, warning it risks undermining European allies who rely on the treaty to hold Russian accountable for its military activities in the region.
Russian Deputy Foreign Minister Alexander Grushko told state news agency Tass a US withdrawal would be "yet another blow to the system of military security in Europe, which is already weakened by the previous moves by the administration".
On Friday, France said it regretted the United States' decision to leave the treaty, although it also shared concerns over Russia's behaviour.
In a joint statement with 9 other European countries, including Spain and Germany, the French Foreign Ministry said the treaty remains "functional and useful".
Cover image: An Open Skies aircraft parked at Offutt Air Force Base, Nebraska, in 2018 (Picture: US Department of Defense).