Kidnappers grabbed six Filipino workers off a merchant ship Saturday in the latest hostage-taking in Nigeria's restive southern oil-producing region, officials said.

The vessel was heading to the oil port of Warri with a crew of 14 when unidentified gunmen boarded and took away the six non-Nigerians, Delta state spokesman Ozoene Sheddy said. Initial reports said seven foreigners were taken, but that proved incorrect, Sheddy said.

Militants seeking to pressure the national government into giving more local control over the area's oil resources have stepped up kidnappings since launching a wave of attacks on oil facilities in early 2006 that have cut oil exports by Africa's biggest oil producer 25 percent.

Militant groups behind dozens of kidnappings in recent months couldn't immediately be reached for comment on the latest incident.

Nearly 100 foreign hostages, mostly oil workers, have generally been released unharmed, usually after a ransom is paid. However, a Briton and a Nigerian died in crossfire during a gunbattle between militants and Nigerian security forces trying to free the hostages.

On Thursday, militants released five Chinese hostages and one Italian who had been taken in separate incidents. Two Italians and one Lebanese remained in captivity.

The conflict stems from the deep poverty that afflicts the people of the Niger River delta despite the area's production of tens of billions of dollars in oil revenue every year. Violence has cut oil production below 2 million barrels a day, compared to the previous 2.5 million.

Complete coverage is available in FOXNews.com's Africa Center.