Nigeria ? Militants released photos of what they claimed were seven of nine foreigners kidnapped in Nigeria and threatened more attacks on the West African country’s volatile oil industry and its workers.

The hostages were seized in a Feb. 18 assault on a barge belonging to a U.S. oil company in the Niger Delta’s Forcados estuary. The captives included three Americans.

The militants are demanding a greater share of oil wealth for their impoverished region, which has remained poor despite the large amounts of oil flowing from it. Nigeria is Africa’s top crude producer, exporting 2.5 million barrels a day.

The two photos, sent in an e-mail to reporters, showed seven unidentified men sitting on a bench with a dozen gunmen wearing black masks and camouflage hats behind them. The militants had ammunition belts wrapped over their shoulders and held assault rifles and rocket-propelled grenade launchers pointed in the air.

The militants also released a statement saying the photos were “pictures of our hostages with a section of the unit that secured their capture.”