Four Americans kidnapped by Somali pirates from their yacht last Friday have all been shot dead.

Four US warships were trailing the yacht as it was escorted into port when the crews heard gunfire at around 0600 GMT today.

Military forces boarded the boat, killing two pirates in the process, but discovered that the four Americans had been shot.

A US military statement said: ‘The forces discovered all four hostages had been shot by their captors.

‘Despite immediate steps to provide life-saving care, all four hostages ultimately died of their wounds.’

Analysts from ECOP-Marine, an international organisation that monitors and fights marine crime, believe that an attack against the hostage takers either came from the outside or from the one passenger on board who was trusted to have certain ‘capabilities’.

General James N. Mattis, the head of US Central Command, offered his ‘deepest condolences for the innocent lives callously lost aboard the Quest.’

The US Navy captured 13 pirates, who are now in custody, and found the remains of two others already dead.

Californians Scott and Jean Adam, a retired vet and dentist respectively, had been sailing round the world since December 2004 in their Davidson 58 pilot house cutter, Quest, distributing Bibles to schools and churches in remote destinations en route.

They joined the Blue Water Rally in Phuket, Thailand, before Christmas, but left it last Tuesday to make their own way from India to Oman, with fellow American couple Phyllis Mackay, 59, and Bob Riggle, 67, from Seattle joining them on board.

Quest’s skipper Mr Adam, 68, joined the Cruising Association (CA) last year. A spokesman for the CA described him as ‘a very experienced cruising hand who had a lot of experience in the Middle East.’

The CA has sent a letter of condolencies to the Seven Seas Cruising Association in America, to which Mr Adam and his wife also belonged.

Ten days ago Mr and Mrs Adam sent an email to friends saying that they were going ‘off-radar’ to avoid being tracked down by pirates, but they were boarded 250 miles off the coast of Oman.

Subscribe to Yachting Monthly magazine for all the latest sailing news and reviews.