Suspected drug cartel hit squads have killed three people connected to the American consulate in the Mexican border city of Ciudad Juarez, according to a US official.
The dead include a consulate employee and her husband, both American, and the Mexican husband of another employee, the BBC reports. They were killed as they drove away from a consular event in two separate attacks on Saturday.
United States President Barack Obama sys he is "outraged" by the drive-by shootings.
It is not yet clear if they were specifically targeted, but the US has authorised employees at some consulates to send family members out of the area.
The six consulates are in the border cities of Tijuana, Nogales, Ciudad Juarez, Nuevo Laredo, Monterrey and Matamoros.
Mexico is battling a drug war that has killed 18,000 people since 2006.
Ciudad Juarez is a major flashpoint in the battle between Mexican drug gangs over trafficking routes to the US. More than 2600 people were murdered there in drug-related violence last year alone.