Pirates have hijacked a tanker in the Gulf of Aden off the coast of Yemen, according to a UK maritime safety organisation (UKMTO) and Somali security officials.

The UKMTO said a "vessel was boarded by unauthorised personnel" as it sailed east, adding that other ships were "advised to transit with caution". Officials from Somalia's semi-autonomous Puntland region said the attackers were Somali.

This is the second hijacking of a vessel off the coast of Yemen since May, when the MT Eureka was seized near the port of Qana . Two other ships were boarded by pirates in the Indian Ocean in April.

There have also been several unsuccessful attacks in a region where piracy appears to be making a comeback.

Until three years ago these kinds of incidents had almost disappeared in this area once notorious for hijackings, following a concerted security operation involving several navies.