Armed men seized four foreign oil workers — two Britons, an American and a German — from a nightclub, the latest in a spate of abductions targeting the petroleum industry in Africa's largest crude-producing country.

Militants grabbed the foreigners hours before three Filipino hostages were released early Monday. Most kidnap victims in the delta are returned unharmed.

Nigeria's oil-rich southeastern delta has seen 14 such abductions in the last week. Kidnappings and sabotage attacks by militants, who argue that the impoverished region does not benefit from its oil, have cut Nigerian production by more than 20 percent since the beginning of the year.

A witness saw more than 10 people wearing military uniforms go into the club and drag a group of foreigners away late Sunday.

"They were shooting, and everyone started screaming," said George Ani, a driver in the city who witnessed the kidnapping. "They took some expatriates, but I don't know how many. I lay on the floor of my car until it was finished."

State police spokeswoman Irejua Barasua said Britons Brayan Fogerty and John Gruyan work for construction and military contractor Halliburton Co. and Smith International unit Smith Bits, respectively. Both firms are based in Houston. Barasua had previously said the Halliburton employee was an American.

She said the other captives — American Royce Antony Parait and German Gerhard Ezeth — worked for two other oil industry firms.

Smith International confirmed in a statement that one of its workers was taken hostage, and said it had not been contacted by anyone claiming responsibility.

Barasua did not identify Sunday's hostage-takers and said no arrests had been made.

The nighttime attack occurred as gun shots rang out across the city, keeping residents in their homes. Barasua said the nightclub attack was the center of violence, but that police started shooting in other neighborhoods as a show of force.

The three Filipino oil workers, who were taken last Friday, were released to the Filipino ambassador in Port Harcourt. They work for U.S. oil contractor Michael Baker Corp. of Moon Township, Pa. No ransom was demanded or given, and no group has claimed responsibility.

A spokesman for ship owner Trico Supply said an agreement was being finalized for the release of Norwegian and Ukrainian employees of Trico taken last week.