Armed Pirates opened fire on a Dutch cargo ship a few miles from Port Harcourt, kidnapping the ship’s master and an engineer and stealing cash, a security source and anti-piracy group AKE said on Wednesday.

An AKE statement said the ship, a “Dutch-owned, Curacao-flagged refrigerated cargo vessel”, was attacked on Tuesday around 4.10 p.m. (1510 GMT), the latest in a string of pirate attacks in the oil-exporting Gulf of Guinea.

“Eight armed men boarded and opened fire towards the bridge, stole cash and crew’s possessions, and kidnapped the master and chief engineer before escaping. A third crew member was left unaccounted for,” it said.

“It is likely the two crew members abducted will be held for ransom onshore.”

Pirates off the coast of Nigeria tend to raid ships for cash and cargo rather than hijacking the crews for ransom like their counterparts off the coast of Somalia, but onshore kidnapping is a major business in Nigeria, especially in oil producing coastal areas like Port Harcourt.

A security source working for an oil company in Port Harcourt gave the same details, adding that there were 14 crew on board. One crew member was injured, he added.

“Vessels in the area are advised to maintain strict watch rotas and exercise vigilance at all times,” AKE said, adding that 13 attacks had been recorded off West Africa in 2012 so far, seven of which occurred off Nigeria.

Pirates shot dead the captain and the chief engineer on a cargo ship off the coast of Nigeria on Feb. 13.