Two US embassy employees were shot and wounded when their car came under fire south of Mexico City on Friday, an official from the attorney general's office told AFP.
"The two are from the US embassy," the official said on condition of anonymity, adding that the shooting took place on a highway leading from Mexico City to the city of Cuernavaca.
The pair was taken to a hospital in Cuernavaca, 90 kilometers (55 miles) south of the capital, the source said.
The car had diplomatic plates and other people were traveling with the embassy employees, the official said. Mexican media reports said the vehicle was covered with bullet holes.
After the shooting, the army and the police closed a 10-kilometer stretch of highway as well as access to a wooded area around the scene of the incident.
The US embassy could not confirm the incident.
"We're looking into the reports but cannot provide or confirm details," said US embassy spokesman Alex Featherstone.
Mexico is in the throes of a violent drug war.
More than 50,000 people have died in drug-related violence since President Felipe Calderon deployed soldiers to combat cartels in 2006.
The United States cooperates closely with Mexico under the $1.6 billion Merida Initiative, which provides training for Mexican law enforcement officials as well as equipment to combat drug trafficking.