Two American engineers were taken hostage by Nigerian pirates who attacked their ship in the Gulf of Guinea off the coast of West Africa on early Wednesday, the Los Angeles Times reports.

The engineers were captain and chief of U.S.-flagged oil supply vessel, the C-Retriever, owned by Edison Chouest Offshore, a maritime company based in Cut Off, La. The identities of the two hostages have not yet been released while the State Department and U.S. Embassy in Nigeria investigate the incident.

"We have been concerned by a disturbing increase in the incidents of maritime crime, including piracy, in this area," State Department spokeswoman Marie Harf told the Los Angeles Times.

Piracy and kidnapping in the waters off of West Africa has become a growing concern for years, trading places with the coast of Somalia in East Africa as one of the world's most dangerous sea lanes. So far this year, thirty incidences of piracy have been reported in relation to Nigeria, including two hijackings, according to the International Maritime Bureau (IMB), in comparison to 11 Somalia-related piracy incidences.

Somalian pirates tend to undertake long-term hostage operations in exchange for ransom, while Gulf of Guiena pirates prefer cargo-stealing operations for oil products like gasoline and diesel that they can sell in the region's massive black market, the Christian Science Monitor reports.

Despite its inherent risks, the Gulf of Guinea is one of the most important trade routes for U.S.-imported oil, with nearly 30 percent of all U.S. oil passing through. Back in July, Gulf of Guinea pirates held 24 Indian sailors hostage for a week before releasing them, while last December, five Indian sailors were kidnapped for a month before being let go, along with four Italian sailors in a separate incident around the same time period.

A U.S. official declined to comment to the Los Angeles Times on whether or not the Pentagon is preparing for military action in response to the latest kidnapping.

"At this point, we do not have information that would indicate this was an act of terrorism," Harf told reporters in a briefing, according to Reuters. "Obviously, our concern at this point is for the safe return of the two U.S. citizens."