Police Deputy Superintendent Nnamdi Omoni said police acted on intelligence to attack the kidnappers "den" in an operation that began Saturday and ended Sunday evening.

The kidnappers escaped and no arrests were made although several of the perpetrators were wounded by police gunfire, Omoni said. One of the kidnap victims was in a state of shock and was taken to a hospital for treatment, he added.

Rivers state police spokesman Nnamdi Omoni gave some information about the operation, and said no ransom had been paid.

Release operations

"We secured their release in batches. Five were released yesterday while seven were released in the early hours of today," Omoni said. The remaining two had been released earlier.

"As a result of our pressure on the kidnappers our men had a shootout with them but none of the kidnappers was killed or arrested," he said, without giving further details. "No ransom was paid."

The victims were local employees of an oil industry service company, Nestoil. They were abducted by gunman September 2 near the country's oil capital, Port Harcourt.

Kidnappings of foreigners and locals in Nigeria are common - especially in the oil-rich Niger Delta. Ransoms are the primary motivation and the kidnappers in this case had demanded 100 million naira, or about $322,600 (290,000 euros).

bik/jm (Reuters, AP)