Warri, Nigeria ? Militants launched attacks across Nigeria’s troubled delta region Saturday, blowing up oil installations and seizing nine foreigners, including three Americans. The violence cut the West African nation’s crude oil exports by 20 percent.

The Movement for the Emancipation of the Niger Delta, which claims to be fighting for a greater local share of Nigeria’s oil wealth, said the attacks were in retaliation for assaults this week by military helicopters. The militants threatened more violence on “a grander scale.”

In an e-mail to The Associated Press Saturday, the group claimed responsibility for the raids, including one in which militants abducted three Americans, two Egyptians, two Thais, one Briton and one Filipino.

The attacks began before dawn, when more than 40 militants overpowered military guards and seized the foreigners from a barge belonging to Houston-based oil services company Willbros, which was laying pipeline for Shell, a Willbros official said on condition of anonymity.

In Houston, Willbros spokesman Michael Collier confirmed that nine employees had been taken. “We have not had any communication with those involved. Right now, we’re in the process of contacting the families. The well-being of our people is foremost and we’re trying to keep this situation under control as best we can,” he said.

In other, apparently coordinated violence, militants blew up a major Shell crude oil pipeline near a facility by the western delta’s Chanomi Creek, Shell official Donald Boham said. Militants also claimed they destroyed a state-run pipeline that feeds gas from the Escravos gas plant in the delta to the country’s commercial capital, Lagos. That attack could not be independently confirmed.