KUALA LUMPUR - US warships are monitoring a Japanese tanker which was hijacked by pirates last weekend off the coast of Somalia, a piracy watchdog said yesterday.

"The pirates are still in control of the ship. They are believed to be armed," Noel Choong, the head of the International Maritime Bureau's (IMB's) Malaysia-based Piracy Reporting Centre, said.

The vessel with 23 Korean, Filipino and Myanmar crew sent out a distress call that was relayed to the IMB last Sunday after pirates boarded the ship.

Choong said US warships in the area were observing the tanker which was in Somali territorial waters.

"Yes, coalition warships are monitoring the tanker," he said, but declined to make further comments due to the safety and security concerns for the seafarers.

On Tuesday, the US navy helped the crew of a North Korean cargo vessel regain control of their freighter in a violent struggle after it was captured by pirates off Mogadishu port.

Maritime officials in Nairobi identified the Japanese vessel as the Panama-flagged Golden Mori and said it was seized about eight nautical miles off the Socotra archipelago.

The captain and chief engineer are Koreans, and the remainder of the crew are Filipinos and Myanmar nationals.

Choong said Somali waters were "dangerous to seafarers", and urged ships to keep 200 nautical miles off the coast and to be alert against "small and suspicious boats" that approach their ships.

"In the past two weeks, there have been lots of attacks against ships off the coast of war-torn Somalia," he said.

There have been 31 attacks with one seafarer killed this year compared to 10 attacks and one seafarer killed last year.

The attacks stopped in the second half of 2006 during six months of rule by Islamists, who were eventually ousted by Ethiopian and Somali government troops last year.

Somalia, which lies at the mouth of the Red Sea, has been without an effective government since the ousting of dictator Mohamed Siad Barre in 1991 sparked a bloody power struggle. - Sapa-AFP