LAGOS, Nigeria -- Pirates off Nigeria's coast attacked a cargo ship Monday, killings its captain and chief engineer in the increasingly dangerous waters of the Gulf of Guinea on the west coast of Africa, officials said.

"All crew except the bridge team took shelter in the citadel. Due to the continuous firing the captain and the chief engineer were shot," a notice on the International Maritime Bureau (IMB) official said.

The captain and chief engineer died of their wounds as the pirates sprayed the ship with gunfire, said Cyrus Mody, an official at the bureau.

---

Mody said the bureau had yet to receive additional information about the ship and its crew, though they did contact authorities in Nigeria. A spokesman for Nigeria's navy and the nation's maritime safety agency did not immediately respond to requests for comment Monday.

The killings come as another ship nearby was attacked this weekend and pirates hijacked a tanker ship off the coast of neighboring Benin on Thursday, according to the maritime bureau.

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.

The frequency of attacks, while not as high as off the Somali coast or surrounding Indian Ocean, is on the rise.

Reuters and The Associated Press contributed to this report.