Explosions tore through two oil-company facilities in southern Nigeria on Monday, officials said, as militants pressed ahead with a yearlong campaign for greater regional control of oil funds in Africa's largest producer of crude.

Two separate private security contractors, speaking on condition of anonymity citing prohibitions on speaking to reporters, said an explosion hit an Agip residential compound in Port Harcourt, and Shell oil reported an explosion at company facilities in the city where many foreign oil workers live.

The Movement for the Emancipation of the Niger Delta claimed responsibility for the explosions, warning beforehand that it had planted three car bombs in the region of creeks and swamps where most of Nigeria's petroleum is pumped.

It promised to continue its struggle to boost regional control over oil funds paid to the central government in the faraway capital, Abuja. The groups attacks have already cut one quarter of Nigeria's normal 2.5 million barrel per day oil production.

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"What we are fighting for is resource control and we will not stop until we achieve our objective," the group said in a statement to The Associated Press.

It was unclear if there were any casualties or production cuts. Residents reported hearing explosions and seeing a large plume of smoke rising over the teeming city. Ambulances and fire engines headed toward the bombing sites, they said.

Niger Delta assailants range from militants saying they are fighting for the freedom of their imprisoned leaders and a greater share of oil wealth to criminal gangs demanding ransoms for hostages. Oil-worker kidnappings are common, although most captives are freed unharmed. The government calls the militants criminals, saying they're involved in the illegal sale of crude oil.

Nigeria is the world's 12th largest oil producer and the fifth-largest supplier to the United States.