SEOUL, South Korea (AP) — Unidentified gunmen have kidnapped four South Koreans and one Nigerian at a construction site in southern Nigeria, a South Korean Foreign Ministry official said Tuesday.

The ministry said the four employees from Hyundai Heavy Industries Co. were at the worksite in Bayelsa state to prepare for the construction of several factories when they were abducted Monday.

Ministry spokesman Cho Tai-young said the armed men initially took away the South Koreans and two Nigerian workers in a speed boat but one local Nigerian was later released.

Cho said there has been no immediate contact from the kidnappers.

Kidnappings for ransoms are frequent in Nigeria’s oil-rich delta. Experts say kidnappers who once targeted mainly expatriate oil workers have shifted their focus to wealthy Nigerian families in recent years.