The United States says it is moving more of its naval forces to the Horn of Africa in response to a hostage stand-off with Somali pirates.
The pirates are holding the American captain of the cargo ship they briefly hijacked in the Indian Ocean.
The gunmen hijacked the Danish-owned, US-flagged 17,000-tonne Maersk Alabama freighter on Wednesday, 645km off the Somali capital Mogadishu.
The 20 American crew retook control after a confrontation, but four gang members continued to hold the captain, Richard Phillips, on the ship's lifeboat after he apparently volunteered to be a hostage for the sake of his crew.
Head of US central command General David Petraeus said the reinforcements would ensure the Navy had all the capability that might be needed in coming days.
General Petraeus did not elaborate, but the BBC reports it is understood two warships are due to arrive in the region by Sunday.
The freighter's operator, Maersk Line Ltd, said the captain was unharmed and securing his safe return was the firm's priority.
The lifeboat is being shadowed by the US warship Bainbridge and naval officers have been talking to the pirates, with guidance from FBI negotiators.
The pirates have also been given food supplies and reported that the captured captain is in good health.
The freed Maersk Alabama is now heading to Kenya under armed guard.
Last year, heavily-armed Somali pirates hijacked dozens of vessels, took hundreds of sailors hostage for weeks and made off with millions of dollars in ransom.
Among the ships seized was a Saudi supertanker with $US100 million of oil on board, and a Ukrainian ship with 33 tanks.
Pirates are currently holding 18 vessels with a total of 267 hostages, many of them from the Philippines, according to the Mombasa, Kenya-based East African Seafarers' Assistance Programme.