International naval forces will never be able to completely secure the vast area of ocean where Somali pirates are hijacking ships off East Africa, the commander of the EU Naval Force's counter-piracy efforts said Tuesday.

In the latest attack, pirates captured the Greek-flagged tanker Maran Centaurus on Sunday while it was carrying 275,000 metric tons of crude oil, the ship's owners said. That is equivalent to about 2 million barrels of oil worth roughly $150 million, said Ben Cahill, head of the Petroleum Risk Manager service at PFC Energy.

The naval commander said the Maran Centaurus was traveling east of an area that the EU Naval Force advises tankers to steer clear of, so that it wouldn't necessarily have expected to have been attacked. Pirates now hold 11 ships and 264 crew members off the coast of Somalia, said Rear Adm. Peter Hudson.

"The news of a few days ago of a 300,000-ton tanker being seized is illustrative of the problems in protecting and policing an area of the world's oceans that amounts to an area of about 1 million square miles," said Hudson, the commander of the EU Naval Force's counter-piracy operations.

Hudson also said the fact that pirates are now attacking ships as far as 1,000 miles (1,600 kilometers) off the Somali coast presents a large challenge and that the EU force will never fully secure such a large area. The EU Naval Force's strategy in the smaller Gulf of Aden is to lengthen the amount of time it takes pirates to get on board so that a warship or helicopter can be dispatched to the scene.

"The difficulties in an area as large as it is in the Indian Ocean with the short number of assets that we have is that ... the pirate can keep going and keep going and keep going until it's successful in getting on board, because there's nothing there to stop it," he said.

Hudson said oil tankers like the Maran Centaurus can be tempting targets.

"She's a big ol' girl, almost a quarter million tons. They're not speedy, they sit low in the water ... so a determined pirate like this one can be successful," Hudson said in Kenya during an extended trip to East Africa.

As pirate activity has increased off East Africa, some ships have begun carrying armed guards. The EU Naval Force said Tuesday that a Spanish fishing vessel with a private security team on board fired warning shots at pirates during an attack Sunday, fending off the hijack attempt.

However, fuel tankers like the Maran Centaurus do not have armed security because of how flammable the cargo is, a determination Hudson said he agrees with.