British fighter jets intercepted two Russian aircraft close to NATO airspace along the alliance’s eastern flank, the U.K. government said on Sunday.

The British Defense Ministry said on Sunday two of its Royal Air Force (RAF) Typhoon jets intercepted an “unknown aircraft” leaving the Russian exclave of Kaliningrad, passing close to NATO airspace on Thursday.

The jets were scrambled from the Malbork Air Base in eastern Poland close to Kaliningrad, the U.K. government said.

Two days earlier, two British Typhoons left the same airbase to intercept a Russian Ilyushin Il-20M intelligence aircraft over the Baltic Sea, the ministry said.

NATO said in late March British Typhoon jets had arrived in Malbork to take up a rotation of the alliance’s enhanced air policing mission alongside NATO’s newest member, Sweden.

This is a developing story and will be updated.