YENAGOA, Nigeria - Militants armed with guns and dynamite invaded an oil services base in Bayelsa state in Nigeria's southern oil-producing Niger Delta on Wednesday and kidnapped nine South Korean workers and one Nigerian.

The security situation is worsening in the delta, which accounts for all oil production in OPEC member Nigeria, the world's eighth-biggest exporter of crude. A fifth of Nigerian output capacity is shut down because of militant attacks.

The attack on the base operated by South Korea's Daewoo Engineering and Construction came less than a week after five Chinese telecom workers were kidnapped for ransom in another area of the volatile delta. Daewoo confirmed that nine of its employees, all South Koreans, had been captured.

"The militants entered the facility armed with guns and dynamite before dawn," said Han Sang-ho, a Daewoo employee at the site, speaking to South Korean TV network YTN.

"There was an exchange of gunshots and they broke in with dynamite," Han said.

The 10 men taken captive were in one section of the living quarters. There were 17 South Koreans in total at the facility, which is located in the Bayelsa state capital Yenagoa.

Hostages in the Niger Delta are usually kept for a few days in remote settlements accessible only by boat through mangrove-lined creeks, before being released unharmed after their employers or local authorities pay money.

However, one Nigerian and one Briton were killed last year in separate botched attempts by troops to free them.

Crime and militancy flourish in the lawless delta, where residents complain of neglect and marginalisation.

The armed forces are unable to control thousands of remote waterways where kidnappings for ransom, politically motivated attacks on the oil industry and theft of crude oil from barges or pipelines are common.

These problems have plagued the delta for years but they intensified in 2006 and many fear violence will further escalate in the build-up to the Nigerian elections in April as armed thugs sponsored by local politicians come back into action.

As well as the Korean and Chinese captives, three Italians and one Lebanese employed by Italian oil company Agip have been held hostage since December 7 in the delta by a rebel group, the Movement for the Emancipation of the Niger Delta (MEND).

The MEND, which says it is fighting for local control of oil assets and reparations for neglect and pollution, was responsible for a wave of attacks on the oil industry last February that shut down over 500,000 barrels per day in output.

The group did not immediately respond to a question about whether it was involved in the attack on the Daewoo base.

On Tuesday, the body of a Nigerian naval officer who was kidnapped two days earlier was recovered. It is not clear who had abducted him or how he died.