A US warship has arrived off the Somali coast where pirates have taken a US ship's captain hostage.

The US-flagged Maersk Alabama was briefly hijacked by pirates on Wednesday but the crew of 20 Americans managed to retake control of the vessel and are trying to negotiate Captain Richard Phillips's release, second mate Ken Quinn said.

Mr Quinn said the four pirates sank their own boat when they boarded the container ship, but the captain managed to talk them into getting off the freighter and into the ship's lifeboat with him.

The crew then overpowered one of the pirates and sought to exchange him for the captain, Mr Quinn said.

"We kept him for 12 hours. We tied him up," he said. The crew eventually released their captive to the other pirates, but the exchange did not work and the captain is still being held by the pirates on the lifeboat.

Mr Quinn said they are now trying other ways to free Captain Phillips. "We are just trying to offer them whatever we can, food, but it is not working," he said.

The Danish-owned freighter's operator, Maersk Line, said the US Navy destroyer Bainbridge had arrived on the scene.

Spokesman BJ Talley said the company was in touch with its ship and is also talking with the navy. But he declined comment on what action, if any, the navy might take.

The boat in which the captain is being held is very near the Maersk Alabama, whose crew can see the navy destroyer and has been in contact with the navy.

A spokesman for the company said no injuries had been reported for the rest of the crew left aboard.

Maritime officials said the Maersk Alabama was carrying food aid for Somalia and Uganda from Djibouti to Mombasa, a Kenyan port, when it was seized far out in the Indian Ocean.

The ship seizure, about 300 miles off Somalia, is the first time Somali pirates have seized US citizens.

The seizure is the latest in a wave of pirate attacks. On Monday, gunmen from Somalia seized a British-owned ship after hijacking another three vessels over the weekend.

In the first three months of 2009 just eight ships were hijacked in the strategic Gulf of Aden, which links Asia, the Indian Ocean and the Red Sea to Europe via the Suez Canal.

Last year, heavily armed Somali pirates hijacked dozens of vessels, took hundreds of sailors hostage - often for weeks - and extracted millions of dollars in ransoms.

Foreign navies sent warships to the area in response and reduced the number of successful attacks.

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