The US has restricted official activities and travel to Nogales, a Mexican border city, to essential movement during daylight hours only, citing unspecified threat information.
"We are alerting US citizens of this threat and change in posture," the US mission to Mexico said in a statement.
US officials did not specify the nature of the threat. The mission urged citizens to exercise increased caution, be aware of their surroundings, seek shelter in the event of an incident, and follow instructions from Mexican law enforcement.
Nogales, located in the northern Mexican state of Sonora, is widely known as a busy crossing point with a history of organized crime, smuggling and periodic violence. The state shares a border with US states of Arizona to the north and New Mexico to the northeast.
The US travel advisory designates Sonora as a Level 3 area, meaning travelers should reconsider travel to the region.
