RAF jets were scrambled to intercept a Russian aircraft approaching the Baltic skies, in the first such intervention as part of their latest mission to keep airspace there secure.
The Typhoon fighter jets were launched from Amari air base in Estonia, after the Russian military transport aircraft did not transmit a recognised identification code and appeared to be unresponsive.
Defence Secretary Michael Fallon described it as an "act of Russian aggression".
He said: "This is another example of just how important the UK's contribution to the Baltic Air Policing Mission is. We were able to instantly respond to this act of Russian aggression - demonstration of our commitment to Nato's collective defence."
Four RAF jets were deployed to join the Baltic Air Policing mission - which sees Nato members help others who do not have their own policing capabilities - last month and will remain there until the end of August.
One of the pilots involved in the mission said it went smoothly.
They said: "The scramble went exactly as planned, we launched our Typhoon aircraft quickly and then using our advanced sensors and mission systems, combined with support from our Battlespace Managers on the ground, carried out textbook intercepts of the three aircraft."
Wing Commander Gordon Melville said: "We have once more proven our ability to secure the skies in the vicinity of the Baltic States and have demonstrated the close link between the Royal Air Force, Estonian and Nato units that have planned and enabled this defensive response so successfully. We will continue to standby 24/7 to secure the Baltic skies."
During the last mission Typhoon fighter jets were scrambled 17 times, intercepting more than 40 Russian aircraft.