A member of the crew of a stricken Canadian submarine has died.
The sailor was airlifted from the vessel in the Atlantic and taken to the nearest hospital after his condition deteriorated mid-flight.
But an MoD spokesman said tonight: "It is our understanding that he has died."
The Canadian Prime Minister Paul Martin said: "He gave his life serving his country and we owe his family our deepest condolences."
Doctors were treating the sailor at Sligo General Hospital in the Republic of Ireland, after a Royal Navy helicopter took him and two of his injured colleagues ashore.
They were airlifted off of the stricken ship and were forced to land at the nearest hospital after the man's condition rapidly deteriorated.
The trio were among nine casualties who suffered smoke inhalation after a blaze broke out on the HMCS Chicoutimi when it was 100 miles off the west coast of of Ireland.
British forces mounted a comprehensive operation to go to the Chicoutimi's rescue, after the captain of the vessel called for help at 3pm yesterday, but have been battling against "treacherous" weather conditions.
A spokeswoman for the hospital tonight said the three men had landed on the helideck at around 8.30pm and were rushed into accident and emergency.
She described one of them as being in a "very critical" condition, while the other two had managed to walk through the doors of the hospital.
The MoD said the Sea King had planned to take the crewmen to Londonderry for medical treatment, but had been forced to make an emergency landing at Sligo.
"The condition of one of the men deteriorated and gave us cause for concern," said the spokesman.
"A medical decision based on his condition was taken to put down in Sligo. The helicopter landed as quickly as it could."
The other two men being treated at Sligo were said to be in a "stable" condition.
News of the man's death tonight broke as rescue tugs neared the stricken vessel.
The tugs, the Anglian Prince and Carolyn Chouest, were due to reach the Chicoutimi today. The small helicopter carrier HMS Argus was also due at the scene.
They will join three vessels already on the scene. The Royal Navy's HMS Montrose was the first vessel to arrive at around 1.30pm yesterday, while a second Royal Navy vessel, HMS Marlborough from Devonport in Plymouth, and the Royal Fleet Auxiliary's Wave Knight, laden with food and fuel and carrying a medical team and helicopter, arrived later.
However, the Canadian navy do not expect the tugs to be able to attempt to rescue the Chicoutimi - which still has 54 crew on board - until tomorrow.
High seas and gale-force winds meant there might not be a chance attach a tow line to the stricken submarine until Friday, said Lieutenant Commander Denise Laviolette.
"Because of the weather conditions out there - we still have six-to-eight metre waves and 35 knots winds, so it's still pretty much a gale - there might not be a window of opportunity until Friday to try to get a tow line to her.
"We have a weather system coming through early Friday morning over here - around lunchtime in Britain - that would abate the waves and wind.
"We're continuously assessing the situation, but right now it seems to be the most likely option to tow her back to Faslane."Reuse content