An RAF plane is "conducting activity" off the Scottish coast, the Ministry of Defence says, amid reports of a Russian submarine being spotted in the area.
A Royal Navy Frigate and submarine are also thought to be involved in the search, along with Canadian and French maritime patrol aircraft.
The Telegraph reports the French plane has searched for the submarine for at least 10 days.
The RAF currently has no maritime patrol aircraft of its own.
But according to the BBC's defence correspondent Jonathan Beale, this lack of patrol aircraft is expected to be addressed in Monday's Strategic Defence and Security Review.
The submarine was detected north of Scotland. The Ministry of Defence did not confirm it was looking for a foreign submarine.
"We can confirm that allied maritime patrol aircraft based at RAF Lossiemouth for a limited period are conducting activity with the Royal Navy," a statement said.
"We do not discuss the detail of maritime operations."
There have been previous concerns that Russia could be developing plans to have submarines sever key internet communications during future wars, following a spike in its naval activity near the locations of undersea cables.