Nine South Korean oil workers abducted from an oil services base in Nigeria's southern delta were freed unharmed on Friday after three days in captivity, a government spokesman said, Reuters reported. On Wednesday, gunmen in six boats invaded the riverside base in Bayelsa state and kidnapped the nine men after blowing up part of an office building. "The Korean hostages have been released," a spokesman for the Bayelsa state government said. "They were released unharmed this evening and they have been handed over to their employers." The nine were working for South Korea's Daewoo Engineering and Construction, which is working on a pipeline project in Bayelsa state, when they were kidnapped apparently for ransom. Their abduction happened less than a week after five Chinese telecom workers were kidnapped for ransom in another area of the lawless delta, which accounts for all the 2.5 million barrels of oil per day output of the world's eighth biggest exporter. The Chinese workers are yet to be released. 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. One Nigerian and one Briton were, however, killed last year in separate botched attempts by troops to free them. Crime and militancy flourish in the delta, where residents complain of neglect and marginalisation. Nigerian security forces are unable to control thousands of remote waterways where kidnappings for ransom as well as politically motivated attacks on the oil industry and theft of crude oil from barges or pipelines are common. Three Italians and one Lebanese employed by Italian oil company Agip have been held hostage since Dec. 7 in the delta by the militant Movement for the Emancipation of the Niger Delta. The group, 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. But it said it was not responsible for the kidnap of the Koreans and the Chinese.