Two crew members of a British nuclear submarine were killed Wednesday in an accident on board, the Ministry of Defence says.

The early morning accident aboard HMS Tireless, which occurred during a joint U.S.-British naval exercise in the Arctic, did not involve its nuclear reactor or weapons systems, the ministry said in a statement.

HMS Tireless is shown during an exercise in the Arctic Ocean on Saturday.
(U.S. Navy, Erik Reynolds/AP)

Initial reports suggest the accident involved a piece of air-purification equipment in the forward section of the submarine.

"The submarine was never in any danger; its nuclear reactor was unaffected, it quickly surfaced and is completely safe," the ministry's statement said.

Tireless, a hunter-killer submarine, does not carry nuclear missiles, it said.

Another submariner was airlifted to a U.S. military hospital with non-life-threatening injuries and is expected to make a full recovery.

Tireless was launched in 1985, but the machinery in question was fitted as part of an update in 2001, the ministry said.

Canada has also felt the human cost of submarine accidents.

On Oct. 5, 2004, a fire broke out on HMCS Chicoutimi as it was on its way to Halifax from Scotland. Several submariners were injured, and Lieut. Chris Saunders later died of smoke inhalation.