Mogadishu: The high-seas shoot-out that left four Americans dead after their yacht was hijacked in the Indian Ocean was provoked by the US navy's intervention, Somali pirates said on Wednesday.

The US military said that four Americans onboard a yacht sailing from India to Djibouti captured on Friday had been killed by their pirate captors on Tuesday.

"We got information that the American hostages were killed after the US navy stormed the yacht," a senior commander from the pirate lair of Garacad, in Somalia's northern self-declared state of Puntland, said.

"They tried to rescue the hostages but unfortunately heavy gunfire was exchanged and they (the hostages) died as a result," the pirate, who asked to be named only as Ali, told the media.

He did not further elaborate on the exact circumstances of the four hostages' death.

According to Vice Admiral Mark Fox, head of the US Naval Forces Central Command based in Bahrain, two of the pirates had been brought onboard a nearby US warship to conduct negotiations to free the hostages.

Then Tuesday morning, with 'absolutely no warning', the pirates launched a rocket-propelled grenade at the warship, the USS Sterett, though several Somalis also raised their arms in surrender on the yacht's deck, Fox said.

US Special Forces raced to the yacht on small boats. By the time they boarded, they heard gunfire and saw that all four Americans had been shot, Fox said. They died after efforts to treat them failed. He said two pirates were killed in the assault.

Abdi Yare, a top commander in Hobyo, currently the main piracy hub in Somalia, rejected the US military's version of events, stressing that pirates have only ever been after ransoms and never shoot their hostages unprovoked.

"We are very surprised by the news of the hostages' death," he said by phone, adding that a scenario in which the hostages were killed by US bullets should not be ruled out.

"What I know is that pirates would never gun down their hostages without a reason and it can't be ruled out that they were caught in the crossfire," said the pirate boss.

"The Americans have attempted reckless rescue operations before and now they have done it again," he said.

Most of the hundreds of hijackings that have occurred off the Somali coast over the past three years have been resolved through the payment of a ransom, albeit after sometimes protracted negotiations.

The 15 surviving pirates from Tuesday's clash are being held on a US ship and will eventually face judicial action 'to hold them accountable', Fox said.

Just last week, a US judge sentenced a teenage Somali pirate to nearly 34 years in prison for his part in the 2009 hijacking of another US ship, the Maersk Alabama. That incident had a more successful outcome for US special forces, who freed the ship's captain, Richard Phillips, in an operation that killed three pirates.

In another deadly military intervention, French forces launched a commando operation to free a yacht held by pirates in 2009 and rescued a small child and his mother but killed his father.

The multi-billion-dollar naval deployments in the region have failed to stem piracy, which is currently at an all-time high, with more than 40 vessels and 800 hostages in pirate hands.

According to Ecoterra International, an NGO monitoring maritime activity in the region, many more yachts are currently waiting for a safe opportunity to cross the Indian Ocean. The Dutch organisers of a Thailand to Turkey convoy of some 30 yachts have complained that their demands for naval protection have been either rejected or ignored.

They argued that the death of the four Americans was also the result of the world's anti-piracy operations neglecting the yachting community.