Summary:
A US diplomat has been shot dead in Mexico, Mexican officials say.

Full article:
(CNN) -- Unknown gunmen attacked an American diplomatic vehicle south of Mexico City, injuring three people, a Mexican military official told CNN Mexico. The motive behind the attack on the U.S. vehicle, which was on a diplomatic mission, was not immediately known. Gunmen inside what was described as a Mexican federal police vehicle fired upon a U.S. Embassy vehicle, said the official, who declined to be named for security reasons. The Mexican official said three Mexican marines were injured in the shooting. However, there were conflicting reports. Some Mexican reports stated that two of the injured were Americans. The injured passengers were transported to a hospital in Cuernavaca, Mexico. The Drug Enforcement Administration confirmed that a U.S. diplomatic vehicle was "shot up" in Mexico, but said no DEA officers were involved in the incident. The U.S. State Department said it was aware of the reports, but had no immediate comment. The U.S. vehicle was attacked on a highway between Mexico City and Cuernavaca, near the town of Tres Marias. Mexico's federal police said that its personnel were not involved in the shooting. Their forces appeared at the scene only after the shooting to secure the perimeter, police said. CNN's Jill Dougherty and Terry Frieden contributed to this report.