Four South Korean employees of Hyundai Heavy Industries, who were abducted earlier this week in Nigeria, have been released, local media reported on Saturday, quoting unnamed government officials in Seoul.
The four hostages had been handed over to South Korean officials in the African country late on Friday, Yonhap news agency and YTN TV said.
There was no immediate comment from either the South Korean government or Hyundai Heavy Industries.
Gunmen kidnapped the four working on Hyundai's operations in the Niger Delta region on Monday.
Kidnapping is rife in Africa's top oil producer, making millions of dollars a year for criminal gangs. It is common across the south, especially in the Niger Delta.