With two tankers seized by Somali pirates in recent days ship owners warned that hijackings are "spinning out of control" and could disrupt global oil supplies if governments don't take tough action against the sea bandits.

"If piracy in the Indian Ocean is left unabated, it will strangle these crucial shipping lanes with the potential to severely disrupt oil flows to the United States and to the rest of the world," said Joe Angelo, managing director of the International Association of Independent Tanker Owners.

"We want to see a significant increase in government will to eradicate piracy in this area and not just contain it."

Piracy is costing the global economy $7 billion-$12 billion a year, the shipping industry says.

The recent tanker seizures took place in the Indian Ocean, one 900 miles east of the pirates' traditional hunting grounds in the Gulf of Aden. It links the Mediterranean and Red seas to the Indian Ocean and is used by some 30,000 ships every year.

On Feb. 8, pirates hijacked the Italian tanker MV Savina Caylyn south of India and 800 miles east of Somalia, the Italian navy reported. The vessel, with a capacity of 105,000 tons and a 22-man crew, was bound for Malaysia carrying Sudanese oil valued at $60 million.

The following day, pirates seized the 270,000-ton Greek-flagged supertanker Irene SL 200 miles east of Oman and nearly 900 miles from Somalia. It was carrying 2 million barrels of Kuwaiti crude to the U.S. Louisiana Offshore Oil Port in the Gulf of Mexico and could be the most valuable vessel the pirates have captured since they began their attacks three years ago.

Angelo said the Irene SL's cargo represented roughly one-fifth of the United States' daily crude imports.

The cargo is worth some $200 million at current prices. That's about twice as much as the oil carried by the Saudi supertanker Sirius Star seized in November 2008.

The pirates got $9.5 million for the release of the South Korean tanker Samho Dream in 2010. They currently hold 32 ships with 725 hostages.

Angelo's warning underlined how the maritime scourge is expanding geographically toward another piracy-plagued area: the Straits of Malacca between Malaysia and the Indonesian island of Sumatra. That 500-mile narrow waterway is the gateway between the Indian Ocean and Asia.

The Somalia pirates' thrust eastward is partly due to the presence of international naval forces in the Gulf of Aden.

The pirates' growing capability to undertake long-range operations, even in the stormy monsoon seasons, has taken them to waters not systematically patrolled by naval forces.

For some months they've been using trawlers and other merchant vessels they capture as "mother ships" for pirate crews who use 20-foot skiffs to carry out attacks. Intertanko says pirates are using more than 20 seized vessels in this way.

On Feb. 6, two Indian naval vessels captured one of these mother ships, a Thai trawler called the Prantalay 11, along with 20 pirates off southwest India when they went to aid a Greek freighter under attack.

The Prantalay was one of three Thai fishing boats seized by pirates off Somalia in 2010.

By moving eastward, the Somali marauders are operating in an area of very rich pickings by hitting shipping lanes used by supertankers, like the Irene SL, carrying oil and natural gas to Asia. That's the main market these days for Persian Gulf oil.

Tankers loaded with large amounts of oil are increasingly valuable prizes with oil prices topping $100 a barrel.

"The hunters are following their prey," said Lt. Cmdr. Jimmie Adamsson of the European Union's anti-piracy task force known as EU Navfor.

There have been growing demands for the naval patrols to use greater force against the pirates. But most task forces, whether U.S.-led, European or independent national flotillas, operate under heavy restrictions.

When force has been used, it has sometimes resulted in the deaths of hostages or captured crewmen.

In November 2008, the Indian navy, which appears to be prepared to use force against the pirates more than most navies, blew up a hijacked Thai fishing boat being used as a pirate mother ship to prevent the marauders escaping. Fourteen of the 15 Thai crewmen were killed.