NAIROBI - SOMALI pirates have released a Panama-flagged Japanese-owned ship hijacked in the Gulf of Aden three months ago, an organisation monitoring piracy in the region said in a statement on Friday.

'The MT Chemstar Venus, sea-jacked on 15 Nov 2008 was released' late on Thursday, the non-governmental group Ecoterra International said.

The ship's crew of 18 Filipinos and five South Koreans are unharmed.

Ecoterra said the last pirates left the ship at 10.30pm (1930 GMT, 3.30am Singapore time) after a ransom was delivered to the vessel by a tug-boat.

The MT Chemstar Venus is owned and managed by the Japanese company Iino Marine and carries some 20,000 tonnes of oil products.

The latest release brings to at least 11 the number of foreign vessels still held by Somali pirates. A total of more than 170 seamen are held hostage.

Some 2,000 Japanese ships sail through Somali waters to cross the Suez canal each year and the Asian giant's shipping industry has voiced alarm over the cost incurred should vessels have to opt for a safer but longer route.

Tokyo late last month ordered its navy to prepare for deployment in the Gulf of Aden and Indian ocean.

Japanese warships will be joining a growing fleet of foreign navies patrolling what has become the world's most dangerous waters, with more than 130 attacks by Somali pirates in 2008 alone.

Japan is restricted by its post-World War II pacifism, with domestic law allowing the navy to use force to protect only ships flying the Japanese flag or carrying Japanese passengers.

According to experts, a slightly lower rate of successful pirate attacks since the start of 2009 is due to a combination of weather conditions and increased navy surveillance. -- AFP