Somali pirates have hijacked a Greek-flagged tanker off the coast of Somalia, a regional maritime official confirmed on Tuesday.

Andrew Mwangura, the East Africa's Coordinator of Seafarers Assistance Program (SAP) said the MV Irene E.M. was seized in the Gulf of Aden before dawn but could not confirm the nationalities of the crew on board.

The overnight attack is the latest attacks on the world's most dangerous waters which came days after several pirates were killed by US and French forces.

Reports from the EU Maritime Security Center said the Irene, a 35,000-ton Greek-owned vessel, was seized overnight.

The center said the 22-man crew is believed to be unhurt and shipping has been warned to stay clear of the area for fear of further attacks.

The seizure came soon after US navy forces rescued Richard Phillips, an American cargo ship captain, on Sunday by killing three young pirates who held him captive in a powerless lifeboat for five days.

A fourth pirate surrendered after seeking medical treatment for a wound he received in trying to take over Phillips' vessel, the Maersk Alabama.

The attacks occur despite dozens of warships from a number of countries, which are patrolling the Somali coastline and have been dispatched as a deterrent, but there is no way they can cover the large swath of the Indian Ocean in which pirates operate.

Seven pirates have been killed in the last seven days by the US and French navies, but that does not seem to have stopped their crimes.

Sources said over fishing has deprived the Somalis of a vital food source and they reacted by forming their own rag-tag "coast guard" whose aim is to arrest and "tax" foreign vessels in their waters.

The international efforts have so far foiled hundreds of attempts to hijack merchant ships in the 800 km-long waterway. While Somali pirates seized nearly 38 percent of the vessels they targeted in 2008, their success rate in the first two months of this year plummeted to about 13 percent due to the strong presence of naval ships.

However, there are still 14 vessels and about 200 crew members currently under the control of pirates, according to the International Maritime Bureau based in Kuala Lumpur, Malaysia.

In 48 hours between April 4 and 6, five ships were hijacked, some of them in the Gulf of Aden heavily guarded by naval forces.

The attacks show the patrols by warships have not been an effective deterrent measure in the war on piracy since the bandits are determined to make money at whatever cost.

According to Jane Campbell, a spokeswoman for the US Navy's 5th Fleet based in Bahrain, it would take 60 naval ships to adequately guard vessels traversing the Gulf of Aden, far beyond the number of the warships now deployed in the area.

(Xinhua News Agency April 14, 2009)