Hijackings are an ongoing problem in the busy shipping lanes off the coast of Somalia.
At least a dozen ships have been seized in the Indian Ocean and more than 200 crew members are being held.
US pirate trial
Meanwhile, a Somali teenager suspected of piracy and allegedly linked to the hostage taking of Richard Phillips, an American ship's captain, arrived in the United States to face charges over the incident.
Abdi Wali Abdulqadir Muse was handcuffed and had a chain wrapped around his waist.
His left hand was heavily bandaged from the wound he suffered during the clashes on the ship two weeks ago.
Muse is the first person to be tried in the US on piracy charges in more than a century.
He was flown to a New York airport and taken into custody ahead of a court hearing on Tuesday.
A law enforcement official familiar with the case said that the teenager was being charged under two obscure federal laws that deal with piracy and hostage-taking.