Officials are warning U.S. citizens not to drive at night in parts of the western Mexican city of Guadalajara after suspected drug-gang members burned vehicles and blocked streets. A separate U.S. alert said the northern city of Monterrey has seen a significant increase in armed robberies at restaurants and convenience stores.

Some of the blockades in Guadalajara took place on a highway leading to the city's airport and to Lake Chapala, a popular retirement and vacation spot for U.S. and Canadian citizens.

The U.S. consulate in Guadalajara, Mexico's second-largest city, posted a message on its website saying that it had prohibited U.S. diplomatic personnel from traveling the highway to the airport at night, and that it "recommends that U.S. citizens consider similar precautions."

Such alerts have been issued in the past for highways in northern and western Mexico, but are uncommon for Guadalajara, which is not considered one of the focal points of an drug war that has claimed more than 34,600 lives since 2006.

The consulate's message advised motorists encountering roadblocks to get off the highway immediately and take shelter in a shopping mall, hotel or any other business they could find nearby. It also included some creative driving tips. "If you are presented with an imminent threat on the road, do not hesitate to run over any median (or similar obstacle) to make an emergency U-turn to get out of harm's way," the message said.

The advisory issued by the U.S. consulate in Monterrey warned of an increase in armed robberies at restaurants, cafes and convenience stores in that city.

The robberies have been carried out by a small armed group that guards the entrance and takes purses, wallets, phones and other valuables from customers inside, the consulate said. None of the robberies has resulted in violence or kidnapping, the advisory said.