Kidnappers in Nigeria's southern oil region have released a British man and a Bulgarian man after a month in captivity.

British and Bulgarian officials say the men were freed Wednesday. Authorities gave no details of the circumstances of the release.

The men, both workers for a British oil company Exprogroup, were kidnapped July 8 from a river barge near the city of Calabar.

Kidnappings and violence have become common in the Niger Delta region since last year, when militants began a campaign aimed at directing more of the region's oil wealth to impoverished locals.

Witnesses Wednesday reported a third straight day of gunbattles between rival gangs in the regional capital, Port Harcourt. A police official is quoted in local media as saying eight people have been killed in the fighting.

Since January 2006, more than 200 foreign workers or their family members have been kidnapped in the Niger Delta. Most have been released unharmed.

Some kidnappings are carried out by militants, while others are the work of gangs seeking ransom.

Some information for this report was provided by AP and Reuters.