Lagos - Oil workers in Nigeria's oil-producing Niger Delta went on strike Monday to complain about a lack of protection from militant groups who attack oil facilities and kidnap workers.

Several hundred employees of oil company Total picketed the company's office in Port Harcourt despite union officials delaying industrial action due to begin Monday, local media reported.

Militant groups often attack oil installations and kidnap expatriate workers in the Niger Delta, saying they are fighting for a greater share of profits from oil exploitation for the poor of the region.

The government says they are merely criminal gangs intent on stealing oil and extorting money.

Main militant group the Movement for the Emancipation of the Niger Delta (MEND), which recently called off a long-term ceasefire, said it had attacked a gas plant over the weekend.

The group also said that wife of former oil minister Edmund Daukoru was released on Friday after a ransom of 2.5 million dollars was paid.

MEND said it was not involved in the kidnapping, but it had information that the ransom was paid after the group holding Gladys Daukoru threatened to "gang rape her every day."

The unrest has cut oil production by around a fifth since early 2006. (dpa)