Staff working at US consulates in towns along the Mexican border were told they could evacuate their families home following the killing of three people leaving a consular party in the city of Ciudad Juarez.
President Barack Obama condemned the killings, which raised the possibility of a new tactic in the violence associated with the Mexican government's US-supported war on the country's drug barons.
In two separate attacks, minutes apart, in broad daylight on Saturday afternoon, two cars leaving the house of a US consular employee were targeted by gunmen. In one, the husband of a staff member was murdered and two children were left injured. In the other, an American staff member and her husband were killed. Their baby was left crying in the back seat.
Ciudad Juarez has become one of the deadliest places in the country as rival drug barons battle for control of territory along the border with their lucrative US market, and the Mexican government, under President Felipe Calderon, attempts to restore control. Some 4,600 people have been killed following drug battles in the city in two years.
The White House's national security council spokesman said "the president is deeply saddened and outraged by the news", and that Mr Obama "shares in the outrage of the Mexican people at the murders of thousands in Ciudad Juarez and elsewhere in Mexico".
Mr Calderon also issued a statement of condemnation as details of the killings were released yesterday, and he promised to dedicate more resources to improving security.
The US told diplomatic staff in border towns including Tijuana, Ciudad Juárez and Monterrey y Matamoros that they could evacuate their families for the next month. If Saturday's victims are found to have been deliberately targeted because of their links to the consulate in Ciudad Juarez, it will be the first attack on American interests since a mortar was thrown into the consulate grounds in Monterrey in 2008.Reuse content