US Navy special forces freed an American ship's captain by killing three Somali pirates who held him hostage in a lifeboat, ending a five-day standoff but risking more violent confrontations off the waters of east Africa.

The life of cargo ship captain Richard Phillips was in danger when Navy snipers aboard a US destroyer shot his Somali captors on Sunday, freeing him unharmed and killing three of four pirates who had held him after trying to seize his vessel, the Navy said. The fourth pirate was in custody.

A Navy commander made a split-second decision to fire on the pirates because he believed that Phillips, who tried to escape on Friday, faced imminent danger amid tense hostage talks with his captors and deteriorating sea conditions.

'They were pointing the AK-47s at the captain,' Vice Admiral William Gortney, head of the US Naval Central Command, said in a Pentagon briefing from Bahrain.

'The on-scene commander took it as the captain was in imminent danger and then made that decision (to kill the pirates) and he had the authorities to make that decision and he had seconds to make that decision.'    

President Barack Obama granted the Pentagon's request for standing authority to use appropriate force to save the life of the captain, Gortney said.

The US Navy 5th Fleet in Bahrain said the rescue took place at 12:19 p.m. EDT (1619 GMT) and the lifeboat had drifted to about 20 miles (32 km) from lawless Somalia's coast.

Phillips, captain of the US-flagged Maersk Alabama container ship, contacted his family after the rescue, received a routine medical evaluation, and was resting comfortably aboard the amphibious assault ship USS Boxer.

'We are all absolutely thrilled to learn that Richard is safe and will be reunited with his family,' said Maersk Line chief executive John Reinhart.

A smiling Phillips was shown in a picture released by the Navy after his rescue. Phillips' crew set off flares, hoisted an American flag and jumped for joy at the news of their captain's rescue.

'We are very happy. He's a hero,' one crew member of the Maersk Alabama shouted at journalists amid raucous celebrations on the deck of the vessel, docked in the Kenyan port of Mombasa.

Phillips, 53, was the first American taken captive by Somali pirate gangs who have marauded in the busy Gulf of Aden and Indian Ocean shipping lanes for years.

Asked about fears that the pirates could now decide to act more violently, Gortney said: 'Yes, there's second and third order effects to every action and this could escalate violence in this part of the world, no question about it.'    

Obama, spared another thorny foreign policy crisis to add to his problems with the US economic meltdown and the war in Afghanistan, welcomed the rescue, praised the US military and vowed to curb rampant piracy.

'To achieve that goal, we must continue to work with our partners to prevent future attacks, be prepared to interdict acts of piracy and ensure that those who commit acts of piracy are held accountable for their crimes,' he said in a statement. - Reuters