Private security officials say pirates have hijacked a fuel tanker and kidnapped foreign sailors in a West Africa region that is experiencing increasing pirate activity.

Security officials said Tuesday that the hijacking of the MT Matrix I happened Saturday off the coast of Bayelsa state in Nigeria. The officials said the pirates kidnapped both Nigerian and Pakistani sailors in the attack.

A military spokesman in the delta referred calls for comment Tuesday to Nigeria's navy, the Associated Press reports. Commodore Kabir Aliyu, a navy spokesman, said there had been no report of a hijacking made to officials.

Some shippers in the region don't report hijackings publicly, out of fears of having their insurance premiums rise.

Telephone numbers for Pakistan's High Commission in Abuja, Nigeria's capital, could not be immediately connected Tuesday.

Nigerian naval authorities listed the ship as one of several allowed to bring subsidized gasoline into the country in May as part of a program costing the nation billions of dollars a year.

Naval officials listed the ship as being operated by a company called Integrated Shipping Services Nigeria Ltd. Other registries listed the ship as being operated by Val Oil Trading SA of Athens, Greece. Phone numbers for both companies could not be found. Officials at Matrix Energy Ltd., a Nigerian company listed as doing business with Val Oil Trading, did not immediately return a call for comment.

Oil tanker hijackings have happened more and more in recent months, with pirates stealing the fuel onboard, as opposed to kidnapping sailors for ransom. Estimates suggest pirates likely are able to make as much as a $2 million profit for off-loading 3,000 tons of fuel. Foreign hostages still draw tens of thousands of dollars in ransoms, with nearly all released unharmed after their companies pay for their freedom.

Insurers have listed Nigeria, neighboring Benin and nearby waters in the same risk category for hijackings as Somalia.

Security experts told The Economist that 2013 could be the worst year ever for pirate incidents off West Africa.

There have been 28 reported incidents this year so far, while 2012 had 62 and 2011 had 44.

Meanwhile, in Somalia, pirate activity has been sharply reduced because of foreign intervention, The Economist reports.

The Associated Press contributed to this report.