Four Somali pirates have recaptured an American hostage after he tried to swim to freedom, and officials say the situation is growing tenser as a U.S. warship and pirate vessels sailed to the area.

The pirates who have taken a sea captain hostage in a lifeboat in the Indian Ocean have shown they are willing to use gunfire to control their captive, and have indicated they will kill him, if provoked by U.S. forces.

Capt. Richard Phillips, the commander of a U.S.-flagged cargo ship the pirates attempted to hijack earlier this week, attempted to swim away from his captors around midnight on Thursday.

U.S. Defense Department officials say Phillips jumped off the lifeboat, located nearly 500 kilometres off Somalia's Indian Ocean coast, and began swimming away. But he was quickly recaptured.

They do not believe the 53-year-old sea captain from Underhill, Vt., was harmed in the incident.

The pirates fired shots from an automatic weapon during the escape attempt, but it was not clear if the shots were aimed at Phillips or into the air.

The USS Boxer, the flag ship for the multinational anti-piracy task force will be nearby the hostage scene soon, Defense officials say. The ship has a crew of 1,000 and carries about two dozen helicopters and attack planes.

U.S. Central Command chief Gen. David Petraeus said, "We want to ensure that we have all the capability that might be needed over the course of the coming days."

The pirates are trying to link up with other vessels, which are holding German, Russian and Filipino hostages, and then get Phillips into Somalia.

But a Somali man who helped negotiate a pirate ransom last year, told The Associated Press that the pirates expect to receive a ransom for Phillips and say they will kill him if they are attacked.

The pirates want to get Phillips to shore, in order to gain a better negotiating position and they are receiving instructions from a pirate leader on the ground in Somalia, he said.

Nick Davis, founder of the Gulf of Aden Group Transit security and coordination centre, said the pirates are motivated to keep the captain safe and in their custody.

"They will not want to hurt him," he told CTV Newsnet on Friday morning in a phone interview from London. "He is the pawn in all of this, he is the negotiating tool."

The raid

The sea captain's attempted escape was the latest development in a tense standoff that has developed since the pirates retreated from the Maersk Alabama -- a 17,000-ton cargo ship they unsuccessfully tried to take over on Wednesday.

The pirates initially held the ship for several hours. But they were forced to abandon their takeover when they were later overpowered by 20 crew members on board the ship.

When the invaders fled, they took Phillips hostage in a lifeboat.

In the hours that followed, the pirates have watched as their lifeboat ran out of fuel, a U.S. destroyer closed in on their position, a U.S. surveillance aircraft surveyed the scene from the sky and FBI hostage negotiators became involved in their standoff.

On Friday, negotiations were ongoing between the captain of the Bainbridge and the pirates on board the lifeboat.

Davis said the pirates have demanded money and safe passage to Somalia.

Pirate reinforcements

"The pirates have summoned assistance -- skiffs and motherships are heading towards the area from the coast," an unnamed Nairobi-based diplomat told to AP on Friday. "We knew they were gathering yesterday."

Mohamed Samaw, a Somali resident who claims to own a "share" in a recently hijacked, British-owned ship, told AP that four foreign ships are headed for the lifeboat.

The pirates have 54 international hostages on board two of the ships, whom they will be using as bargaining chips. Samaw said a seized German cargo ship is among the ships moving towards the lifeboat.

Former FBI agent Jack Cloonan told AP that having other hijacked vessels arrive in the area "could complicate the negotiation strategy under way."

And the situation already is tense enough with the U.S. warships that are sailing towards the scene.

Abdi Sheikh, the Mogadishu Bureau Chief for Reuters, told CTV Newsnet that the pirates "are afraid to be bombed by the American warship."

The Maersk Alabama left the area on Thursday, protected by armed Navy SEALs who will ride with the cargo ship until it arrives at its destination port in Mombasa, Kenya, on Saturday night.

It was the sixth ship to be hit by pirates in the same week.

Because pirates have been able to repeatedly extort multimillion-dollar ransom fees from shipping companies, such attacks have become an ever-more common phenomenon.

Davis said pirates, like those involved in the current standoff, care little about the turmoil they cause for their hostages.

"They have no respect for anybody or anything else they just want the money to be able to change their own lives," he said.

With files from CTV Newsnet and The Associated Press