Somali pirates have freed a chemical tanker and its 23 Filipino crew members after holding them hostage for more than five months.

Captain Dexter Custodio, spokesman for the Sagana Shipping Company, which owns the MT Stolt Strength, said the vessel had been released on Tuesday.

According to the East African Seafarers' Assistance Programme, the ship had been carrying a cargo of phosphoric acid from Dakar, Senegal, and was en route to Kandla in India with its Filipino crew.

It was seized in November by pirates in the Gulf of Aden.

It is not known whether a ransom has been paid.

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.