A group of armed Islamist militants is reportedly headed to a Somali port Friday to attack pirates holding hostage a massive Saudi Arabian oil tanker.

Ships belonging to Muslim countries should not be seized, Abdelghafar Musa, a fighter with the Islamist group al-Shabab, told the Associated Press.

This undated picture taken at an unknown location shows the Saudi oil supertanker MV Sirius Star, which has been hijacked by Somali pirates. ((Christian Duys/Associated Press) )

"We are really sorry to hear that the Saudi ship has been held in Somalia. We will fight [the pirates]," Musa, who claims to speak on behalf of all Islamic fighters in the Horn of Africa nation, told the Associated Press Television News.

Somali pirates captured the Sirius Star last weekend about 450 nautical miles southeast of Kenya's Mombasa port. It's believed to be anchored in the port of Haradheere, about midway up Somalia's coastline.

Islamist fighters also reportedly arrived at the Somali port of Haradheere seeking information on the Sirius Star, said a local elder.

"The Islamists arrived searching for the pirates and the whereabouts of the Saudi ship," said the elder, who declined to be named.

"I saw four cars full of Islamists driving in the town from corner to corner. The Islamists say they will attack the pirates for hijacking a Muslim ship."

Islamist leaders, fighting a two-year insurgency against the government and its Ethiopian military allies, deny allegations they collude with pirates and insist they will stamp down on them if they win power.

Islamists in control of southern Somalia

Somalia has not had a functioning government since 1991. When an umbrella Islamic group, which included the al-Shabab, controlled most of southern Somalia for six months in 2006, there were few reports of piracy.

That umbrella group has now split, but Islamist groups have taken control of large portions of southern Somalia in recent weeks, and al-Shanab reputedly holds the largest share.

The United States views al-Shabab as a terrorist organization with ties to al-Qaeda militants who were allegedly behind the 1998 bomb attacks on U.S. embassies in Kenya and Tanzania that left over 230 dead.

Some analysts, however, say Islamist militants are benefiting from the spoils of piracy and arms shipments facilitated by the sea gangs.

The supertanker, which is roughly 330 metres long and three times the mass of a U.S. aircraft carrier, is carrying $100 million US worth of oil. The ship — itself worth about $100 million — has a crew of 25 people from the Philippines, Saudi Arabia, Croatia, Poland and Britain.

The pirates have asked for $25 million in ransom, according to unconfirmed reports.

Pirates holding 330 hostages

Cmdr. Jane Campbell, with the U.S. Navy's 5th fleet in Bahrain, said hijacked ships are docked in four or five ports along Somalia's coastline. Roughly 330 merchant mariners from 25 different countries are being held hostage, she said.

The Gulf of Aden, off the coast of Somalia, has become a hot spot for pirate attacks. ((CBC)) Pirates have conducted attacks in a nautical area covering 2.8 million square kilometres, she said.

While the high-profile hijacking of the Sirius Star has thrust the issue into the spotlight, Campbell insists the success rate for pirates in the region is dropping. In August, sea pirates had a 53 per cent success rate, she said.

That same month, the military started advising shipping companies on simple ways to prevent piracy, including how to train lookouts and quickly alter their course.

That, along with an increased military presence in the Gulf of Aden, resulted in October's success rate dropping to 31 per cent, she said.

Campbell said the problem of sea piracy must be dealt with on land through diplomatic, economic or military means.

"Piracy is not something that will be ended on the high seas," she said.

UN votes for sanctions

Countries have taken action to clamp down on the attacks. The United Nations Security Council voted unanimously on Thursday to impose sanctions on anyone engaging in or contributing to violence in the country.

Sanctions against an accused party would include the freezing of assets and a travel ban, although the 15-member council did not define which individuals or entities would be affected. That is expected to be decided later by a sanctions committee.

The British-drafted resolution also targets anyone obstructing delivery of humanitarian assistance to Somalia, where hundreds of thousands have been forced from their homes.

The African Union is pressing the UN to speed up sending peacekeepers to Somalia, and one of the world's largest shipping companies has announced it will send some of its 50 oil tankers around the Cape of Good Hope in South Africa rather than navigate the Gulf of Aden.

Other shipping companies, including Norway's Frontline Ltd., which transports much of the Middle East's oil to areas around the world, were considering similar moves.

Roughly 11 per cent of the world's seaborne petroleum passes through the Gulf of Aden, where NATO, the United States, Russia, India and several other countries have warships patrolling on anti-piracy missions. Reports from India Friday suggested the Indian navy may further increase its presence in the Gulf.

Earlier this week, an Indian warship, the INS Tabar, sank a suspected pirate "mother ship" in the Gulf and chased two attack boats.