France and Britain may have to cooperate more closely on underwater patrol routes after two of their nuclear-armed submarines collided because they are quieter than shrimps, France's defence minister said on Tuesday.

Defence Minister Herve Morin denied the sophisticated submarines, which are hard to detect, had been shadowing each other deliberately when they collided this month in the Atlantic and described it as a freak accident.

"There's no story to this -- the British aren't hunting French submarines, and the French submarines don't hunt British submarines," Morin told Canal+ radio

"We face an extremely simple technological problem, which is that these submarines are not detectable. They make less noise than a shrimp".

He said the submarines' mission was to sit at the bottom of the sea and act as a nuclear deterrent.

Making clear the allies would try to ensure the collision is not repeated, Morin said: "Between France and Britain, there are things we can do together....one of the solutions would be to think about the patrol zones."

Defence analysts have said the accident could have resulted in a disaster if the hulls had been ruptured because this could have set off conventional ammunition or started a fire.

The French navy initially said its submarine, Le Triomphant, had suffered light damage after hitting a submerged object, probably a container.

But both countries confirmed on Monday that the submarine had collided with Britain's HMS Vanguard, which carries the Trident nuclear missile.

Morin denied any attempt at a cover-up. He said Britain and France had been able to exchange information on the incident only after the Vanguard returned to base.

Le Triomphant is armed with 16 nuclear missiles. France and Britain each have four nuclear-armed submarines.