Britain said two Royal Air Force (RAF) Typhoon jets were scrambled from Romania to investigate suspected Russian fighter aircraft operating near NATO airspace over the Black Sea.
The typhoons took off from a Romanian base near Constanta to shadow the two suspected Russian Su-30 Flanker aircraft, the RAF said in a statement.
RAF jets regularly monitor Russian warplanes near U.K. airspace, and the encounter near Romania is the second in that area since July.
The Royal Air Force has deployed Typhoons to the Baltic States in recent years as part of a mission to protect NATO airspace in the region.
Britain's Minister of State for the Armed Forces, Mark Lancaster, spoke about "an ever more assertive Russia" in a speech in London in July.
He said the RAF has had to scramble jets more than 80 times over the last decade to intercept Russian military aircraft.