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 Tuesday.

The Greek-flagged tanker Maran Centaurus was carrying more than $20 million of crude oil when pirates captured it Sunday.

Rear Adm. Peter Hudson said Tuesday he does not advise vessels to have armed guards on board, and that flammable cargo and firearms don't mix.

Hudson also said the fact that pirates are now attacking ships 1,000 miles off the Somali coast presents a large challenge and that the EU force will never fully secure such a large area of ocean.

Twenty percent of global shipping — including 8 percent of global oil shipments — is funneled into the narrow, pirate-infested Gulf of Aden that leads through the Red Sea to the Suez Canal. The route is bordered on one side by the failed state of Somalia and on the other by the increasingly unstable country of Yemen.

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. At current market rates the oil would be worth just over $20 million.

The ship has 9 Greeks, 16 Filipinos, 2 Ukrainians, and a Romanian aboard. Granberg said the ship's owner reported the crew was not injured in the attack.

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.