Two US embassy staff have been shot by Mexican police in what is believed to be a case of mistaken identity.
Both have been taken to hospital, according to reports, though their injuries are not thought to be life threatening.
A Mexican police official, speaking on condition of anonymity, said one suffered a wound to the leg and the other was hit in the stomach and hand.
The official said the wounded were not agents of the Drug Enforcement Administration or FBI, but did not identify which agency they work for.
The Mexican public security ministry and marines said in a statement on Friday: "A diplomatic vehicle belonging to the US embassy was hit by multiple bullets from personnel of the federal police in the Tres Marias-Huitzilac highway."
The shootings appeared to have been the result of a confused running gun battle that broke out on a rural road in a mountainous area that has been used by common criminals, drug gangs and rebels in the past.
A Mexican army official said the SUV with diplomatic plates was found after a report about a shoot-out on the two-lane road.
He added that a Mexican navy captain was also in the vehicle, but was not injured.
The Toyota car was riddled with bullets, most concentrated around the passenger-side window.
The scene was cordoned off and guarded on Friday by more than 100 heavily armed marines and soldiers and the road was closed.
Investigators examined what appeared to be shell casings left at the scene.
Attacks on diplomatic personnel were once considered rare, but this is the third attack in two years.
In 2011, one US Immigration and Customs Enforcement agent was killed and one wounded in a drug gang shooting in northern Mexico.
And a drug gang shooting in 2010 in the border city of Ciudad Juarez killed a US consulate employee, her husband and another man.