NAIROBI, Kenya (AP) — An oil tanker bound for the United States that was hijacked by Somali pirates was traveling outside a recommended maritime corridor, the commander of the EU Naval Force said today.

The Greek-flagged tanker Maran Centaurus was carrying 275,000 metric tons of crude oil when pirates captured it Sunday.

Rear Adm. Peter Hudson said today that the vessel was the second-largest ever hijacked by pirates, and that the ship was traveling outside of a corridor in which the EU Naval Force recommends that ships travel.

“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.

Hudson also said that the EU force will never fully secure such a large area of ocean.

“We will never close down on a piece of ocean that large — pirate skiffs and pirates who are determined to operate up to 1,000 miles off the coast of Somalia. We just need to be alive to that reality,” Hudson said.

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 that time constraint is not there. 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.

As pirate activity has increased off East Africa, some ships have begun carrying armed guards. The EU Naval Force said today 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.

Fuel tankers like the Maran Centaurus do not have armed security because of how flammable the cargo is.

Pirates now hold about a dozen vessels hostage and more than 200 crew.

“At the moment the consensus is, and I think quite rightly, let’s be very wary before we bring military groups, armed guards, civilian guards onto fuel tankers full of fuel and gas,” he said.

Bigger tankers like the Maran Centaurus are too large to use the Suez Canal and must sail south around Africa to Europe or the U.S., said Samuel Ciszuk, an analyst for IHS Global Insight. But if attacks increase, those tankers will have to steer clear of a large part of the northwest Indian Ocean and southwest Arabian Sea, adding days to the trip.

“This translates into somewhat higher operational costs for the wages and keep of the crew on board as well as fuel for the carrier. A greater cost increase, however, is likely to be the insurance premium, which is a relatively large moveable cost in the overall crude shipping operation,” Ciszuk said.

Somalia’s lawless 1,880-mile coastline has become a pirate haven. The impoverished Horn of Africa nation has not had a functioning government for a generation and the weak U.N.-backed administration is too busy fighting an Islamist insurgency to go after pirates. Pirates now hold about a dozen vessels hostage and more than 200 crew members.

The Maran Centaurus is carrying around 275,000 metric tons of crude, said Stavros Hadzigrigoris, from the ship’s owners Maran Tankers Management.

The vessel is only the second oil tanker captured by Somali pirates. The Saudi-owned Sirius Star was hijacked a year ago, leading to heightened international efforts to fight piracy off the Horn of Africa. That hijacking ended with a $3 million ransom payment. The ship held 2 million barrels of oil valued at about $100 million and was released last January.