PARIS (Reuters) - The French navy detected a Russian submarine carrying nuclear missiles in the Bay of Biscay in January, Obs magazine reported on Thursday, citing a senior French official.

According to Obs, the submarine, from the Murmansk base, did not enter France's territorial waters, but was seen off France's Atlantic coast.

A spokesman for the French navy neither confirmed or denied the information saying it was a general policy not to communicate on such matters.

"Russian naval activity has been on the rise for several months, if not years, and we are permanently attentive to it," the spokesman said.

Russia has flexed its military muscle over the past couple of years, amid heightened tensions between the West and Moscow over Ukraine, and the NATO military alliance has repeatedly reported more incursions by Russian fighters and long-range bombers into its airspace.

In Britain and Sweden patrol planes have searched their waters over the past two years after the sighting of a submarine's periscope and reports of foreign "underwater activity".

In mid-February French and British fighter jets intercepted two Russian Tu-160 bomber planes heading toward British airspace near the French coast.

(Reporting by Marine Pennetier and John Irish; Editing by Alison Williams)