Police and oil company officials in Nigeria's oil-producing Niger River Delta region say militants have released at least seven workers who were taken hostage over the past week.
The officials say the hostages were released Wednesday in two separate groups.
Two of the captives were Nigerian employees of Royal Dutch Shell oil company taken hostage Saturday as they repaired a pipeline. The second group included five foreign workers taken from an oil rig a week ago.
Nigeria's Police Chief Mike Okiro has ordered a crackdown on gangs responsible for kidnappings in the oil-producing region.
Some 200 foreign workers have been abducted since the end of 2005, making criminal kidnapping widespread in Nigeria's main oil-producing region.
Reports from the region say increased security may be disrupting the criminal activity.
Okiro says he ordered senior commanders to clamp down on gangs in the region, and that thousands of security personnel have been deployed to the area.
Some abductions are the work of criminal gangs seeking ransom, while others have been carried out by militants demanding that local villages get more of the region's oil wealth.
Most Niger Delta residents are impoverished, despite the billions of dollars the government and oil companies reap from oil production.
Some information for this report was provided by AP and Reuters.