MOGADISHU/WASHINGTON - A U.S. Navy destroyer arrived off Somalia on Thursday to apply pressure for the release of an American ship captain taken hostage in the first seizure of U.S. citizens by increasingly bold pirates.

Gunmen briefly hijacked the 17,000-tonne Maersk Alabama freighter on Wednesday, but the 20 American crew retook control after a confrontation far out in the Indian Ocean, where pirates have captured five other vessels in a week.

The four gang members were holding the captain on the ship's lifeboat and the crew were trying to negotiate his release.

Our main concern remains the safe return of the captain and our latest communications with the ship indicate that he is unharmed, said B.J. Talley, spokesman for the Danish-owned freighter's operator, Maersk Line Ltd.

The U.S. warship Bainbridge arrived on the scene before dawn on Thursday, the company added. The Federal Bureau of Investigation (FBI) said it had been called in to assist, and its negotiators were fully engaged.

U.S. Secretary of State Hillary Clinton said the lifeboat now appeared to be out of fuel.

We are surrounded by warships and don't have time to talk, one of four pirates on the lifeboat told Reuters by satellite phone. Please pray for us.

The attack was the latest in a sharp escalation in piracy in the waters off lawless Somalia, where heavily armed sea gangs hijacked dozens of vessels last year, took hundreds of sailors hostage and extracted millions of dollars in ransoms.

The long-running phenomenon has disrupted shipping in the strategic Gulf of Aden and busy Indian Ocean waterways, increased insurance costs and made some firms send their cargoes round South Africa instead of the Suez Canal.

The upsurge in attacks makes a mockery of an unprecedented international naval effort against the pirates, including ships from Europe, the United States, China, Japan and others.

PIRATES HOLD CAPTAIN AS SHIELD

Pirates say they are undeterred by the foreign flotilla and will simply move operations away from the patrols.

The solution to the problem, as ever, is the political situation in Somalia, said analyst Jim Wilson, of Lloyds Register-Fairplay. Somalia has had no effective central control for 18 years.

Until there is peace on land there will be piracy at sea.

Maersk said its crew regained control of the Alabama on Wednesday when the pirates left the huge ship with one hostage, the ship's captain, Richard Phillips. The rest of the crew were unhurt.

The ship was carrying thousands of tons of food aid destined for Somalia and Uganda from Djibouti to Mombasa, Kenya, when it was attacked about 300 miles off Somalia.

We are just trying to offer them whatever we can, food, but it is not working too good, second mate Ken Quinn told CNN of efforts to secure their captain's release. He said the four pirates sank their own boat after they boarded the Alabama.

Then the captain talked the gunmen into the ship's lifeboat with him. The crew overpowered one of the pirates and sought to swap him for the captain, Quinn told CNN.

We kept him for 12 hours. We tied him up, Quinn said. They freed their captive, he added, but the exchange did not work.

In Haradheere port, a pirate stronghold, an associate of the gang said the gunmen were armed and ready to defend themselves.

Our friends are still holding the captain but they cannot move, they are afraid of the warships, he told Reuters. We want a ransom and of course the captain is our shield. The warships might not destroy the boat as long as he is on board.

Pirates there said two boats full of gunmen had left the port to go and support their surrounded colleagues.

We are afraid warships will destroy them before they reach the scene, one told Reuters.

On Monday, Somali gunmen captured a British-owned ship after hijacking another three vessels over the weekend.

We think the world must come together to end the scourge of piracy, Clinton told reporters in Washington, saying she was following the saga closely.

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