The high-seas drama involving an American ship captain held hostage by Somali pirates entered its fourth day Saturday with both pirates and U.S. forces moving reinforcements to the scene off the Horn of Africa. The pirates have threatened to kill Capt. Richard Phillips if the U.S. 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 U.S.-flagged Maersk Alabama freighter, which was carrying food aid for hungry people in Somalia, Rwanda and Uganda, according to a report of Associated Press. 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.