Gunmen have kidnapped three Chinese workers at a hydro-electric damn project in central Nigeria, with two local workers killed after clashes between the gang and security forces, police officials said on Thursday.

Criminal gangs looking for ransom payments are often said to target expatriate workers at infrastructure projects in parts of Africa’s most populous nation.

Suspected armed bandits on Tuesday afternoon attacked “workers comprised of some Chinese expatriates and local staff” at the Sino-Hydro project in Niger State who were working on a transmission line tower, state police spokesman Wasiu Abiodun said in a statement. 

“Police tactical team attached to the facility engaged the hoodlums in a gun duel while four of the expatriates were rescued with one of them and two local staff sustaining bullet injury,” Abiodun said.

“In the process of scampering for safety during the gun duel, three among the expatriates were abducted.”

The two local staff died later in hospital, the statement said.

Chinese employees have been targeted several times in Nigeria over the last few months as they work on multi-billion-dollar infrastructure projects that include mining, railways, airports and roads. Victims are usually released after a ransom is paid although authorities rarely confirm if money changes hands.