DES MOINES, Iowa (KCCI) —

An Iowa family of four that went missing while on vacation in a popular Mexican tourist area died from asphyxiation caused by inhalation of toxic gases, authorities said Saturday.

CBS News reports that the Quintana Roo Attorney General’s office said that forensic doctors determined the Sharp family was dead for approximately 36-48 hours before they were found. The type of gas or where it came from was not specified. The Attorney’s General office said that firefighters carried out an inspection of the “gas installation of the room.”

There was no sign of violence where the family was found.

The Sharp family was reported missing by relatives in their hometown of Creston early Friday, about a week after the family left for vacation.

Creston police said they contacted the U.S. Department of State, and the bodies were found during a welfare check at the condo in Akumal near Tulum.

Union County authorities said the family members were identified as 41-year-old Kevin Sharp; his wife, 38-year-old Amy Sharp; and their children, 12-year-old Sterling and 7-year-old Adrianna.

The State Department’s website, which was updated last month, advises Americans in Mexico to “exercise increased caution due to crime.”

Homicides in the region where the resort is located, Quintana Roo, have increased compared with the same period in 2016, according to Mexican government statistics, and most of the deaths appeared to be targeted, criminal organization assassinations.

The turf battles between the criminal groups have resulted in violent crime in areas frequented by U.S. citizens, the website said.