Fighter jets from the British and German air forces have been scrambled to intercept a Russian plane flying close to Estonian airspace, Britain’s Ministry of Defense said on Wednesday.

Britain and Germany are conducting joint missions to patrol Estonia’s airspace as part of NATO’s efforts to strengthen its eastern flank in response to Russia’s actions.

Britain’s Ministry of Defense said Typhoon fighter jets took to the skies on Tuesday after a Russian refueling plane failed to contact Estonian air traffic control. The Russian plane, however, did not enter the airspace of Estonia, which is a member of NATO, the agency added.

Such interceptions happened often even before Russia invaded Ukraine. NATO planes made about 400 interceptions of Russian planes annually. But the incident came amid heightened tensions following a collision between a Russian plane and an American drone over the Black Sea.

British and German aircraft will jointly patrol the skies as part of NATO’s mission to protect the airspace of the Baltic countries until the end of April.