Updated

UNITED NATIONS -- Somalia's U.N. Mission said Friday that pirates hijacked a yacht carrying four U.S. citizens in the Indian Ocean off the Somali coast.

Omar Jamal, first secretary at the Somali mission, identified the yacht as the S/V Quest.

He said the mission is calling for the immediate release of the hostages and all other captives who are in the hands of the pirates.

Jamal said the hijacking raises "serious concern" as it follows the sentencing in New York on Thursday of a Somali pirate who kidnapped and brutalized the captain of a U.S.-flagged merchant ship off the coast of Africa in 2009. Abdiwali Abdiqadir Muse was sentenced to 33 years in prison.

A website chronicles the voyage of a yacht named S/V Quest describes it as being the home of Jean and Scott Adam. The couple has been sailing around the world since December 2004, according to the website. "This is planned to be an eight or ten year voyage," it states.

Earlier on Friday, The European Union's anti-piracy task force said it appeared that Somali pirates had hijacked a separate vessel, the Alfardous, and its eight crew members in the Gulf of Aden. The force said it had no more details about the vessel since it was seized Sunday.

Somalia hasn't had a functioning government since 1991, and piracy has flourished off its coast.

The pirates earn multimillion dollar ransoms from the hijackings. They were holding 29 ships and roughly 660 hostages before the latest seizures.

Jamal said the mission again appeals to the international community to help curb the ever increasing acts of piracy.