LAGOS, Nigeria – Nigeria's military exchanged fire with armed men in this West African nation's oil-rich delta region, the military said Thursday, in an attack apparently against a militant group holding two American hostages and a Briton.

A militant group holding three foreign oil workers hostage said in an e-mailed statement that one of their vessels was attacked Wednesday on the Escravos River by four Nigerian navy patrol boats, sparking a 45-minute gunbattle they claimed left seven government soldiers dead.

A military spokesman, Maj. Said Hammed, on Thursday confirmed an exchange of fire with armed men, but he gave no further details.

The militants said that “the Nigerian government and military should note that we have sufficient firepower in that vicinity to repel any attack.”

Ethnic Ijaw militants took nine foreign oil workers hostage Feb. 18 and released six of them last week. The remaining three include two Americans and a Briton.

The militant Movement for the Emancipation of the Niger Delta claims to be fighting to win a greater share of oil wealth on behalf of the Niger Delta's impoverished inhabitants, who have remained poor despite the fact that most of Nigeria's oil is being pumped from the swampy region. The government characterizes the militants as criminals and oil thieves.

A wave of militant attacks this over the last two months has forced Nigeria to cut daily exports by 20 percent. Nigeria normally produces about 2.5 million barrels per day.

Militants have threatened more attacks.