The Mexican government has advised migrants driving home from the United States for the winter holidays to form convoys for their own protection inside Mexico

They have also been asked to travel only during daylight hours. The interior ministry said the Mexican army could provide escorts to protect convoys from attack by criminal gangs. Mexico's northern border states are experiencing high levels of drug-related violence, making it dangerous to travel on some major highways. Migrants returning from the United States have in the past been targeted for robbery and extortion because they often bring back new cars, cash and other goods. An estimated 12 million Mexicans live in the United States, and the money they send home is Mexico's second-highest source of foreign income after oil exports. The US State Department has also warned its citizens of the danger of attack while driving in northern Mexico.