An investigation was underway yesterday into the deaths of two British soldiers who were killed in an accident on a nuclear-powered submarine on exercise in the Arctic, the Ministry of Defense said.

Another submariner was also hurt in the accident on board HMS Tireless and he has been airlifted to a US military hospital with his injuries described as not life-threatening.

The ministry said the nuclear reactor on board Tireless, a hunter-killer sub which does not carry nuclear weapons, was not affected. The submarine "quickly surfaced and is completely safe", the MoD said in a statement.