Capt Phillips apparently offered himself as a hostage to save his crew
The US Navy has called in FBI hostage negotiators to help secure the release of a US captain held by Somali pirates in a lifeboat in the Indian Ocean.
Capt Richard Phillips was taken from the Maersk Alabama cargo ship after it was briefly seized by pirates.
Officials said a US warship had arrived in the area and was remaining in sight of the lifeboat during the tense talks.
Relatives of the Maersk Alabama crew told US media the ship was now sailing to Mombasa in Kenya under armed guard.
'Dead in the water'
FBI spokesman Richard Kolko said the navy had called his hostage experts "to assist with negotiations".
He said the FBI was now "fully engaged in this matter".
The pirates took the lifeboat from the Maersk Alabama when they fled the ship after being fought off by the American crew.
Analysts have said the negotiations could be lengthy, with the pirates keen to extract a ransom for the captain as well as compensation for a boat that was wrecked in the attack.
And the lifeboat is thought to be equipped for a week at sea, although the ship's owners, Maersk, said it had run out of petrol and was "dead in the water".
Captain's safe return is 'priority'
"It is floating near the Alabama. It's my understanding that it is floating freely," said Maersk spokesman Kevin Speers.
The cargo ship, carrying food aid destined for Somalia and Uganda, was taken about 500km (311 miles) off Somalia's coast in the early hours of Wednesday.
US Secretary of State Hillary Clinton said the government was following the situation very closely and urged the world to act to end the "scourge" of piracy.
There were 50 hijacks amid 130 incidents last year by Somali pirates, but this was the first time Americans had been seized.
Mohamed Omaar, the foreign minister in Somalia's fragile transitional government, told AP that the pirates were "playing with fire".
He said they had "got themselves into a situation where they have to extricate themselves because there is no way they can win".
Somalia has been without an effective government since 1991, fuelling the lawlessness which has allowed the pirates to thrive.
'A captain's response'
On Wednesday, sailors on the Maersk Alabama managed to give US media dramatic accounts of their day-long battle with the pirates.
According to second mate Ken Quinn, the crew managed to capture one of the pirates and keep him tied up for 12 hours while they attempted to negotiate the release of their captain.
Family members said Capt Phillips had offered himself to the pirates to secure the safety of his crew.
"That is what he would do. It's just who he is and his response as a captain," Gina Coggio, his wife's half-sister, told AP.
Surge in hijackings
The ship was first attacked by several pirate boats in the early hours of Wednesday.
It is not clear how many attackers were involved, but accounts from the sailors on the Maersk Alabama suggest that four boarded the vessel.
Maritime officials said the ship had taken all possible evasive action before it reported that the pirates had boarded.
Pirates typically hold the ships and crews until large ransoms are paid by the shipping companies - last year the firms handed over about $80m (£54m).
After a lull earlier this year, this was the sixth ship seized off Somalia in the past week.
The attacks are threatening to destabilise one of the world's busiest shipping lanes.