S Koreans released in Niger Delta

Insurgents frequently attack the oil industry in the Niger Delta

Nine South Korean oil workers who were taken hostage by gunmen in Nigeria have been freed unharmed, officials say.

The attack took place on Wednesday at a Daewoo oil facility in the southern oil state of Bayelsa. A Nigerian worker was also abducted.

Less than a week before the kidnapping, five Chinese telecom workers were seized by gunmen in another area of the volatile Niger Delta.

Kidnappings for ransom and attacks on the industry are frequent in the area.

South Korean diplomats had been negotiating with the militant group to secure their release.

A company official told South Korea's Yonhap news agency that a negotiation team had met the kidnappers late on Friday.

"The sides reached agreement on the release of the kidnapped workers," he said.

He added that the workers were expected to be handed over to their South Korean employer later in the day.