Gunmen in military fatigues seized two foreign oil workers in southern Nigeria early Thursday, the latest violence targeting the petroleum industry in Africa's largest producer, authorities said.

The workers — a Belgian and a Moroccan — were abducted as they traveled through the southern city of Port Harcourt, where many international energy firms make their bases, Rivers State Police Commissioner Samuel Adetuyi said.

A private security official said the captors wore camouflage uniforms in the style of Nigeria's military. The security worker, citing witnesses, spoke on condition of anonymity due to company prohibitions against speaking to reporters.

Southern Nigeria, where most of the country's crude oil is pumped, has seen an increase in violence against the petroleum industry in recent days. The attacks have forced a nearly 20 percent reduction of Nigeria's usual 2.5 million-barrel daily production, helping send crude prices soaring in international markets.

The abductions came a day after gunmen stormed a supply boat in the Gulf of Guinea heading to offshore oil rigs, kidnapping four Norwegian and Ukrainian workers in a raid on the vessel owned by a Norwegian shipping firm.

CountryWatch: Nigeria

Norwegian Ambassador Tore Nedreboe said the captors apparently were not after a ransom from boat owner Trico Supply, but were using the kidnapping to broker a financial deal with a Nigerian oil company.

"This Nigerian oil company has recently concluded an agreement with a part of the local community, and the kidnappers, they want to be included in that agreement," he said.

Nedreboe would not identify the oil company or give details on what the kidnappers wanted. The Norwegian news agency NTB identified the two Norwegians as ship captain Jarle Johansen, 45, and chief machinist Roger Bjerkaas, 40.

Last week, militants in camouflage uniforms seized a German oil worker in Nigeria's troubled delta region. A group calling itself the Movement for the Niger Delta People claimed responsibility, but police said the group was unknown.

Militants have kidnapped oil workers to bargain for a greater share of the wealth. More than 30 have been abducted this year, including three from Port Harcourt. Most of the kidnappings end peacefully.

The militants say that residents remain deeply impoverished while government officials and oil companies are growing rich.