A Spanish fishing boat with 26 crew on board has been seized by pirates off Somalia, officials in Spain say.

Somali coastal waters are among the most hazardous in the world, despite the presence of US navy patrols.

Grenade launchers

A source from the Basque government's Agriculture, Fisheries and Food department told Spanish news agency Efe that four armed pirates took control of the boat using grenade launchers.

Last year, more than 25 ships were seized by pirates in Somali coastal waters.

Somalia has not had an effective central government for more than 17 years and is plagued by insecurity.