The high-seas drama involving an American ship captain held hostage by Somali pirates entered its fourth day Saturday with both pirates and US forces moving reinforcements to the scene off the Horn of Africa. The pirates have threatened to kill Capt. Richard Phillips if the US attacks them, according to a Somali who has been in contact with the pirates. On Friday, Phillips tried to swim for his freedom but was recaptured. Phillips, of Underhill, Vermont, was seized Wednesday after he thwarted the pirates' bid to hijack the US-flagged Maersk Alabama freighter, which was carrying food aid for hungry people in Somalia, Rwanda and Uganda. The Alabama headed toward the Kenyan port of Mombasa - its original destination - with 20 American crew members aboard. It was expected to arrive Saturday night, said Joseph Murphy, whose son is second-in-command of the vessel. Piracy along the anarchic and impoverished Somali coast, the longest in Africa, has risen in recent years. Somali pirates hold about a dozen ships with more than 200 crew members, according to the International Maritime Bureau, a piracy watchdog group based in Malaysia. The bureau lists 66 attacks since January, not including the Alabama. The US was bolstering its force by dispatching other warships to the site where the lifeboat carrying Phillips was within sight of a US destroyer. He was taken hostage in the pirates' failed effort to hijack the cargo ship Maersk Alabama on Wednesday. The pirates' strategy is to link up with their colleagues, who are holding Russian, German, Filipino and other hostages, and get Phillips to lawless Somalia, where they could hide him and make it difficult to stage a rescue, the Somali said. That would give the pirates more leverage and a stronger negotiating position to discuss a ransom. Anchoring near shore also means they could get to land quickly if attacked. The Somali, who helped negotiate a ransom last year for pirates who seized a Ukrainian ship carrying tanks, spoke on condition of anonymity for fear of reprisals. He said he has talked with a pirate leader in Somalia who helped coordinate the failed effort to seize the Alabama. He said the pirate leader had been in direct contact with the lifeboat via a satellite phone but lost contact after Phillips' captors threw the phone - and a two-way radio dropped to them by the U.S. Navy - into the ocean, fearing the Americans were somehow using the equipment to give instructions to the captain. They acted after Phillips' failed effort to escape. Early Friday, Phillips jumped off the lifeboat and began swimming, according to Defense Department officials speaking on condition of anonymity because they are not authorized to talk about the sensitive, unfolding operations. One of the pirates then fired an automatic weapon, the officials said, although it was not clear if the shots were fired at Phillips or into the air, and he returned to the lifeboat. The USS Bainbridge, which is several hundred yards away, has rescue helicopters and lifeboats but is keeping its distance, in part to stay out of the pirates' range of fire. Its sailors were able to see Phillips moving around and talking after his return to the lifeboat, and the Defense Department officials think he is unharmed. Negotiations had been taking place between the pirates and the captain of the Bainbridge, who was getting direction from FBI hostage negotiators, the officials said. The pirates are businessmen, not suicidal jihadists, said Scott Stewart, vice president for tactical analysis for Stratfor, a global intelligence company based in Austin, Texas. "These are people who are trying to make money," Stewart said. "They want to survive this. They don't want to die, which is a good thing in the captain's favor." US Central Command chief Gen. David Petraeus said US warships were headed to the area, more than 483 kilometers off Somalia's Indian Ocean coast. Defense officials say the USS Boxer, flag ship for a multination anti-piracy task force, will be nearby soon. They spoke on condition of anonymity because they were not authorized to publicly discuss sensitive ship movements. The Boxer resembles a small aircraft carrier. It has a crew of more than 1,000, a mobile hospital, missile launchers and about two dozen helicopters and attack planes. A Nairobi-based diplomat, who spoke on condition on anonymity because he is not authorized to talk to the media, said the pirates have summoned assistance and that skiffs and mother ships are heading towards the area from the coast. Mohamed Samaw, a resident of the pirate stronghold in Eyl, Somalia, who claims to have a "share" in a British-owned ship hijacked Monday, said four foreign vessels held by pirates are heading toward the lifeboat. A total of 54 hostages are on two of the ships - citizens of China, Germany, Russia, Ukraine, the Philippines, Tuvalu, Indonesia and Taiwan. Samaw said two ships left Eyl on Wednesday. A third sailed from Haradhere, another pirate base in Somalia, and the fourth was a Taiwanese fishing vessel seized Monday that was already only 30 miles (48 kilometers) from the lifeboat. Jack Cloonan, a former FBI agent whose Virginia-based firm Clayton Consultants Inc. handles hostage negotiations, told The Associated Press that the presence of other hijacked vessels in the area "could complicate the negotiation strategy under way." "We know for certain that they share information. We know they talk to each other. They're not stupid. They can be very smart," Cloonan said. Phillips, 53, thwarted the takeover of the 17,000-ton US-flagged Alabama by telling his crew of about 20 to lock themselves in a room, the crew told stateside relatives. The crew later overpowered some of the pirates but Phillips surrendered himself to the bandits to safeguard his men, and the Somalis fled with him to an enclosed lifeboat, the relatives said. Officials at Maersk Line Ltd. offices in Norfolk, Virginia, did not respond to repeated messages seeking comment Friday. Capt. James Staples, a classmate of Phillips at the Massachusetts Maritime Academy, said he was not surprised by the escape attempt. "That just shows me that Richie's still ... strong, he's thinking, he's alert," Staples said. "He's going to take every opportunity he can to, to make the situation a lot better for himself and probably get home as quick as he can."