RAF jets were scrambled from a former Fife airbase to intercept Russian air force planes over the North Sea on Thursday night.
The response is the third time in less than a week that the Typhoons have been launched from the former RAF Leuchars base, which is now home to the army.
Pilots from RAF Lossiemouth in Moray are temporarily based at the site.
Officials said the planes were two Russian Air Force Tu-142 Bear F, which are anti-submarine warfare and maritime patrol aircraft.
The Russian planes were identified as they approached the UK’s Flight Information Region but failed to engage with air traffic controllers.
Concerned that they posed a risk to civilian airliners, the RAF were asked to intercept them. However a spokesman for the RAF stressed that neither of the foreign planes entered UK sovereign airspace.
In a statement posted online, they said: “Unidentified aircraft were detected by NATO as they operated within the Alliance’s area of interest. This includes sovereign airspace (over a country’s land mass and 12 nautical miles off their coastline) and the international airspace around it.
3️⃣ Quick Reaction Alert scrambles over the space of 6️⃣ days… it's been busy for #TeamLossie 💪, but we're always…
“The two aircraft approached the UK’s Flight Information Region or FIR. This airspace is managed by NATS, the National Air Traffic Services for the UK, where aircraft operating within it should follow instructions from Air Traffic Controllers. These aircraft were not talking to NATS controllers, and while this is international airspace, this behaviour creates a hazard for other air users including civilian airliners.
“QRA Typhoons were scrambled from Leuchars Station in Fife, and routed to intercept the two aircraft.
“The two Tu-142s were shadowed until they departed the UK Flight Information Region, where Luftforsvaret Quick Reaction Alert (from the Royal Norwegian Air Force) took over the mission of monitoring their activities.
“Danish and French Quick Reaction Alert were also involved with today’s mission, along with a wide range of branches and trades within the Royal Air Force and NATO.”
On Monday, Typhoons were scrambled from Leuchars – resulting in a sonic boom heard across Tayside – as two Russian Tu-160 Blackjacks “operated within Nato’s area of interest”, according to the RAF.
Two days earlier, the fighter jets were sent out in response to two Russian Tu-142 Bear Fs operating near UK airspace.