MEXICO (CBS) – The U.S. State Department has issued a travel alert for the Mexican resort city of Playa del Carmen.

The State Department is warning of a security threat but is not elaborating on what kind of threat it is. Also, the State Department has closed its consular office there and banned U.S. government employees from traveling to the city.

An explosive device was found on a tourist ferry in Playa del Carmen last week. Two weeks before that incident, an explosion on another ferry left 26 people hurt.

Playa del Carmen is a popular spring break destination.