The head of U.S. Customs and Border Protection on Monday said immigration officials are working closely with Mexican authorities to investigate a series of stunning attacks in Mexico including a car bomb in the border city of Juarez that has drawn comparisons to Middle Eastern terrorism.

Bersin said the violence is the result of “civil war” among the cartels.

“We see this as part of an ongoing threat that we’ve been cooperating deeply with the government of Mexico to confront,” he said.

The FBI has dispatched agents to assist Mexican officials in the investigation of the Juarez attack.