This Oct. 25, 1992, photo shows sailors aboard HMS Vanguard, in Holy Loch, Scotland. Nuclear-armed submarines from Britain and France collided in the Atlantic Ocean this month, damaging both vessels but releasing no radioactivity, a British official says. (Chris Bacon/PA/Associated Press)

Two nuclear-armed submarines from Britain and France collided deep under the Atlantic Ocean earlier this month, causing damage but releasing no radioactivity, officials in London and Paris said Monday.

HMS Vanguard, the oldest vessel in Britain's fleet of nuclear-armed submarines, and France's Le Triomphant sub, which was also carrying nuclear missiles, both suffered damage described as minor in the underwater crash.

No crew members were reported injured in the incident, first reported by the British tabloid newspaper, the Sun, on Monday morning.

Britain's most senior sailor, First Sea Lord Adm. Jonathon Band, said the crash posed no risk to the safety of the submarines' nuclear reactors and nuclear missiles. But he offered no explanation of how the rare incident might have occurred.

"The two submarines came into contact at very low speed," Band said in a statement. "Both submarines remained safe."

France's Defence Ministry said the ballistic missile submarines had been carrying out routine patrols when they collided.

"They briefly came into contact at a very low speed while submerged. There were no injuries. Neither their nuclear deterrence missions nor their safety were affected," the ministry said Monday.

Neither Britain nor France would say when the collision occurred.

Damage visible, BBC reports

After the accident, the French submarine returned to its base on L'Ile Longue on France's western tip under its own power, escorted as usual by a frigate, the ministry said.

The BBC reported that HMS Vanguard had to be towed back to a submarine base in Scotland and dents were visible in its hull.

Naval warfare experts said the collision was an astounding event.

"This really shouldn't have happened at all," said Stephen Saunders, a retired British Royal Navy commodore and the editor of Jane's Fighting Ships, "It's a very serious incident and I find it quite extraordinary."

Saunders said Britain and France would probably have let each other know that their submarines were in the same general area, but without giving specific co-ordinates of their vessels.

"The whole point is to go and hide in a big chunk of ocean and not be found. They tend to go around very slowly and not make much noise," he said.

As part of each country's independent nuclear deterrent, submarines stay at sea awaiting orders to fire their atomic weapons in the event of a war.

Politicians, activists demand answers

CBC's Nancy Durham in London says the collision is hugely embarrassing to both countries, which try to maintain tight secrecy about their nuclear weapons.

"This is just the kind of thing we would never have heard of," Durham says, "Britain's Ministry of Defence would have never made an announcement like this but once it got out there in the press this morning, they were forced to comment."

The incident sparked concern among nuclear activists, who have long warned that nuclear-armed submarines pose risks of radioactive leaks into the world's waters.

"This is a nuclear nightmare of the highest order," said Kate Hudson, chairwoman of Britain's Campaign for Nuclear Disarmament.

"The collision of two submarines, both with nuclear reactors and nuclear weapons onboard, could have released vast amounts of radiation and scattered scores of nuclear warheads across the seabed."

She called on British Prime Minister Gordon Brown to end such patrols, which she said have at least one British nuclear sub in the Atlantic at all times.

Opposition political leaders also demanded a full explanation from the government.

Brown "needs to explain how it is possible for a submarine carrying weapons of mass destruction to collide with another submarine carrying weapons of mass destruction in the middle of the world's second-largest ocean," said Angus Robertson of Scotland's pro-independence Scottish National Party.

With files from the Associated Press