MEXICO CITY — Traffic jams are nothing new in Mexico’s largest cities, but drug traffickers intent on frustrating the authorities have added them as a new weapon to their arsenal, blocking city streets and creating long lines of frustrated motorists, law enforcement officials said.

The center of the action last week was the bustling commercial city of Monterrey, where the authorities said criminals commandeered dozens of tractor-trailer trucks and other vehicles on Thursday and Friday to block more than 30 streets and highways. The blockades, called narcobloqueos by the Mexican news media, resulted in traffic chaos, with the trucks parked horizontally across highways and vehicles jammed up behind them.

Luis Carlos Treviño Berchelmann, head of public security for the state of Nuevo León, which encompasses Monterrey, described the blockades as a response by the drug cartels to recent antidrug offensives by the government. Other government officials agreed, labeling the stealing of vehicles and abandonment of them on busy highways as a desperate attempt by drug gangs to show their power.

The chaotic scenes that the criminals created did give the impression they had the upper hand. Local newspapers described young men carrying stones, baseball bats and, in some cases, even more deadly weapons, assaulting drivers and stealing their vehicles, only to leave the cars abandoned at odd angles on roadways. In some cases, the vehicles were shot up or burned.