Gang-related violence sparked the concerns.
The U.S. State Department has widened an existing travel warning on Mexico to extend to the popular tourist region that includes Cancun.
The travel warning issued Tuesday added several regions that had been previously thought to be relatively sheltered from the country's gang violence.
The alert also warns specifically of carjacking, kidnapping, and highway robbery.
The Mexican state of Quintana Roo, which includes the popular resort towns of Cancun, Cozumel, Playa del Carmen, and Tulum, was included in the travel warning, advising that the region had seen an increase in homicides in 2016. The murders were gang related, but bystanders suffered injuries in the gunfights.
"Turf battles between criminal groups have resulted in violent crime in areas frequented by U.S. citizens," notes this section of the alert.
However, seemingly tempering the warning, the alert tells U.S. residents: "Resort areas and tourist destinations in Mexico generally do not see the level of drug-related violence and crime that are reported in the border region or in areas along major trafficking routes."