The US navy has rescued an American captain held hostage by pirates in a lifeboat adrift off the coast of Somalia, ending a tense five-day standoff by shooting dead three of his four captors.

US navy rescued American captain held hostage by pirates in Somalia. Captain Richard Phillips (right) Captain Richard Phillips ( right in photo ), who commanded the Maersk Alabama cargo ship, was rescued when snipers took aim at the pirates on Sunday and after President Barack Obama approved the use of force to save him, the US navy said.

He was in good condition after being held hostage for five days in the lifeboat from the Maersk Alabama after the ship's American crew on Wednesday fought off the pirates' attempt to capture the freighter.

Navy snipers hidden in the rear of the USS Bainbridge, one of two navy warships that rushed to the scene, shot and killed the pirates, said Vice Admiral Bill Gortney, commander of US naval forces in the region.

US navy rescued American captain held hostage by pirates in Somalia The pirates "were pointing the AK-47s at the captain," who was tied up, Gortney told reporters in a teleconference from the US Fifth Fleet headquarters in Bahrain.

The snippers had been given orders to "take decisive action" if Phillips was at risk at any time, Gortney said.

"The on-scene commander thought that the captain was in imminent danger and then made that decision, and he had the authority to make that decision and he had seconds to make that decision," said Gortney.

The snipers fired when they had one of the pirates in their sights "and two pirates with their head and shoulders exposed," Gortney said.

At the time the USS Bainbridge, a guided missile destroyer, was towing the lifeboat to calmer waters and was some 25 to 30 meters ahead of the boat.

Navy SEAL (Sea, Air and Land Forces) commandos were involved in the rescue, Gortney said.

Snipers dropped into sea

According to CNN, the snipers were earlier brought in by helicopter and dropped into the ocean behind the Bainbridge.

The fourth pirate surrendered, Gortney said, adding that the US Department of Justice was "working out the details" on how and where to prosecute him.

US media described the surviving pirate as possibly being 16 years old.

US navy rescued American captain held hostage by pirates in Somalia Although the US government's policy is to not negotiate with pirates, Gortney acknowledged that US officials were engaged in a "deliberate hostage negotiation process" with the pirate aboard the USS Bainbridge.

Phillips was taken aboard the USS Bainbridge then flown to the assault ship USS Boxer, where he was "in good health." He called his family in the United States and received a medical checkup.

In Washington, Obama - who had been publicly silent on the hostage crisis - said in a statement that he was "very pleased" with Phillips' rescue, called it "a welcome relief to his family and his crew."

The United States remains "resolved" to combat piracy off Somalia, Obama said.

Maersk spokeswoman Alison McColl, speaking in Phillips' hometown of Underhill, Vermont, said the captain's wife, Andrea, found her husband in good spirits when they talked on the phone.

McColl said Andrea Phillips and her family were thankful to for "a tremendous amount of support" received since the hostage drama began.

US navy rescued American captain held hostage by pirates in Somalia The 20-crew Maersk Alabama had been bound for Mombasa, Kenya, carrying aid for the UN World Food Program, an agency official told AFP .

It docked safely in the Kenyan port on Saturday and crew members were seen celebrating after hearing of their captain's rescue, shouting and popping open champagne bottles. The crew stayed aboard as FBI agents investigated the ship considered a crime scene.

Pirates threaten revenge

The US operation came two days after French commandos stormed a yacht where other were holding two French couples and a child. The child's father was killed in the operation, while the other hostages were freed.

The captors, who had reportedly demanded US$2 million in ransom, had warned against using force to rescue Phillips.

"The Americans have played the same trick that the French troops did because we lost contact with our friends this afternoon," Abdi Garad, head of the Somali pirate group that held Phillips, told AFP .

Garad said the pirates had dropped their ransom demand and were asking for Phillips to be moved onto a Greek ship that had been hijacked by the group.

"The American liars have killed our friends after they agreed to free the hostage without ransom, but I tell you that this matter will lead to retaliation and we will hunt down particularly American citizens travelling our waters," Garad said by phone from the pirate lair of Eyl.

"We will intensify our attacks even reaching very far away from Somalia waters, and next time we get American citizens... they (should) expect no mercy from us."

Somali pirates have intensified their attacks over the last week, and another group was maneuvering an Italian tugboat and its 16-member crew towards the Somali coastline after it was hijacked Saturday, pirate sources said.