The US State Department has extended its travel warning for Mexico because of concern over drug-related violence.
Three more states have been added to the list of places it says Americans should avoid.
The warning says the states of Michoacan and Tamaulipas, as well as parts of Sinaloa, are all troubled by violence and organised crime.
But the state department also notes that millions of US citizens visit Mexico safely each year.
The state department had previously warned Americans against unnecessary travel to parts of the northern states of Chihuahua, Durango and Coahuila.
The areas affected by the warnings include popular tourist attractions such as the Copper Canyon in Chihuahua and the mountains of Michoacan, where Monarch butterflies migrate in one of nature’s great spectacles.
The state department warning says tourist destinations have not seen the same levels of drug-related violence as the border region and major trafficking routes.
And it says the Mexican government is making a considerable effort to protect US citizens and other foreign visitors.
But it warns that criminal gangs are adopting new tactics, including blocking roads with stolen vehicles to impede the security forces, and hijacking cars. And it says the future timing and location of violent incidents is impossible to predict.
The state department has also extended its authorisation for families of US government staff in consulates in northern Mexico to live in the United States, following the murder of three people linked to the US consulate in Ciudad Juarez in March.
Drug-related violence has left some 18,000 people dead in Mexico since 2006.
During a visit to Mexico in March, US Secretary of State Hillary Clinton pledged increased support for Mexico in the fight against drug gangs.
She said more would be done to cut US demand for drugs and the flow of profits and guns into Mexico.
Tom Costello is the CEO, Partner & Co-Founder of Groups International, a company that provides marketing, consultative services, and technology solutions to the group and leisure travel markets. Connect with him on Twitter, LinkedIn, and Facebook or contact him by email.