ABUJA, May 28 (Reuters) - Kidnappers on Monday released a Polish engineer seized on May 24 in Nigeria's oil-producing Niger Delta, security sources said, but about 23 other foreigners are still in captivity in the anarchic delta.

The Polish man, who is the chief engineer for a dredging company, was seized last Thursday by six gunmen near the port of Warri, security experts working for oil companies said.

Abductions for ransom or to press political demands are frequent in the impoverished Niger Delta, home to Africa's biggest oil industry. About 100 expatriates have been kidnapped this year and most were freed after their employers paid up.

One of the security sources said a Lebanese hostage was also released on Monday, but this could not be confirmed from other sources. Gunmen had seized a Lebanese financial controller working for an oil services company in Warri on May 22.

Oil production from Nigeria, the world's eighth-biggest exporter, is down by about 700,000 barrels per day or almost a quarter because of an 18-month wave of attacks on the industry.

Militants have demanded local control over oil revenues, compensation for decades of oil spills and freedom for two jailed leaders from the delta. They have blown up pipelines and oil wells, planted car bombs and kidnapped foreign workers.

But crime flourishes in the lawless wetlands and most abductions are motivated by money.

AlertNet news is provided by