Somali pirates hijacked a Yemeni tanker carrying more than 2,000 tonnes of diesel in the Arabian Sea on Saturday, Yemen's defence ministry said.
The ship was en route from the Gulf of Aden to the southeastern port of Nashtoon when the pirates attacked it and diverted it to the Somali coast, the ministry said in a brief statement posted on its website.
"Yemeni authorities are conducting contacts to secure the release of the hijacked ship," it said.
No further details on the ship or its crew were immediately available.
The hijack took place two days after Somali pirates released a Yemeni fishing vessel they had held for more than two weeks. The ship was hijacked along with another fishing vessel in the Gulf of Aden Dec 10.
The other ship was released Dec 27, and Yemeni officials said that no ransom was paid for the ship's release.
Brigadier General Ali Rasea'a, commander of Yemen's coastguard force, said in remarks published Friday that the motive behind the hijacking of the two vessels was not ransom.
"The pirates intended to use the ships as mother ships for their attacks on merchant ships crossing the Gulf of Aden," he said.
The Gulf of Aden, one of the world's busiest waterways, remains a hotspot for pirate activities despite increased calls for joint security patrols in the troubled waters. Nearly 20,000 ships pass through the Gulf of Aden each year on their way to and from the Suez Canal.
In 2008, 112 ships were reported to have been attacked by pirates and 42 hijacked. Fourteen of the hijacked vessels and more than 240 crew members are still being held by pirates.