The treaty was designed to reduce tensions between Cold War rivals by curbing military buildups on borders in Europe. But Russia’s exit, along with its war in Ukraine, have made the treaty “unsustainable,” NATO said.

NATO announced on Tuesday that it would suspend the operation of a Cold War-era security treaty after Russia formally exited the agreement.

It’s the latest in a series of rising tensions between NATO and Russia after Moscow launched a full-scale invasion of Ukraine in February 2022.

The Treaty on Conventional Armed Forces in Europe (CFE), which was signed in 1990 and ratified two years later, sought to prevent Cold War rivals from building up military forces and equipment near their mutual borders.

Russia previously suspended its participation in the pact in 2007 and announced its intent to completely withdraw in 2015. Russia’s exit from the agreement was finalized earlier on Tuesday.