Assailants kidnapped five South Korean workers at an oil field in Nigeria on Wednesday, South Korea's Foreign Ministry said, two days after Nigeria's oil minister vowed in Seoul to stop hostage-taking in his country.

The abduction occurred sometime after midnight in Port Harcourt, an oil hub in Nigeria's volatile southern delta region, the ministry said in a statement.

There were 14 South Korean workers at the site, but the other nine escaped and took shelter in a control room, the ministry said. A Nigerian man was also kidnapped.

The incident followed the abductions on Friday of six Britons, one American and one Canadian from an oil platform off Nigeria's southeastern coast. The militants who seized the foreigners were demanding jobs and money. The captives were released two days later.

CountryWatch: Nigeria

Unrest has plagued Nigeria's oil-rich southern delta region for years, and in recent months armed militants have stepped up a campaign against the oil industry, blowing up oil pipelines and kidnapping foreign workers.

The country, which normally pumps 2.5 million barrels a day, is the fifth-largest source of oil for the United States.

On Monday, Nigerian Oil Minister Edmund Daukoru told reporters in South Korea that Nigeria takes seriously the recent spate of kidnappings and would do "everything possible" to stop them.

Daukoru, who is also president of the Organization of Oil Exporting Countries, was in Seoul to meet with officials to promote investment in Nigeria's oil sector.

Three of those abducted Wednesday work for Daewoo Engineering and Construction Co. and two are employed by the state-invested Korea Gas Corp, the South Korean Foreign Ministry said.

Daewoo official Huh Hyun said it appeared money was the motive for the kidnappings and that the company would negotiate with the captors. The official declined to discuss further details.

South Korean President Roh Moo-hyun, on a visit to Africa's largest oil producer in March, signed an energy-cooperation agreement with Nigerian President Olusegun Obasanjo. Nigeria's state oil company and the Korean National Oil Company also signed a deal to collaborate in the exploration of two oil fields in the south.