MEXICO CITY, Mexico » 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 Friday 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.

Hotel managers on Lake Chapala said Friday the warning has not significantly affected business.

The U.S. consulate in Guadalajara, Mexico’s second-largest city, posted a message on its website Thursday 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."

On Tuesday, assailants hurled grenades, burned vehicles and blocked several Guadalajara streets and highways in seven near-simultaneous attacks that injured a policeman and two transportation workers. Such tactics have been used by cartels in the past to aid their escapes from police.

The attacks were staged by drug gangs, possibly in retaliation for the arrests of their members, said Fernando Guzman Perez, interior secretary of Jalisco state, where Guadalajara is located.

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.

Chapala, a shimmering, mountain-ringed lake, has been popular among U.S. and Canadian citizens for decades.

Ricardo Soto, manager of the lakeside Quinta San Carlos hotel, said the drug gangs’ actions this week had affected business "a little."

He said some customers almost didn’t show up because they did not know there were other routes to get to the hotel.

"Once you explain it to them, the people come," said Soto, who noted that the hotel was nearly booked Friday. "This is a wonderful place, and all the problems with drug trafficking haven’t really affected us, because it is all more over toward the airport."

Ricardo Hernandez, who manages the Casa Mis Amores hotel in the nearby lakeside town of Ajijic, said of the problems, "It hasn’t affected us up to now."

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 Friday by the U.S. consulate in Monterrey warned of an increase in armed robberies at restaurants, cafes and convenience stores in that city, Mexico’s third largest.

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.

Monterrey has been affected in recent years by growing drug violence, attributed to a dispute between rival cartels. The consulate’s message didn’t say whether the recent robberies were related to organized crime.

In the western state of Michoacan, gunmen ambushed a police vehicle and fatally shot two state officers as they transported a detainee to the local prosecutors’ office. The detainee was also killed in the attack in the town of Villa Hermosa on Thursday, authorities reported Friday.

Michoacan is a stronghold of La Familia, a brutal drug gang known for staging bold attacks on security forces.