MEXICO CITY — An arson attack on a casino in northern Mexico on Thursday that left 52 people dead has thrown a spotlight on the growth of gambling houses throughout the country and their role in organized crime.

In what President Felipe Calderón called an act of “true terrorists,” armed men in four vehicles — a Mini Cooper leading sport utility vehicles and a pickup truck — calmly drove up to the Casino Royale in Monterrey at midafternoon, dashed inside, ordered people to get out and set it ablaze with a flammable liquid.

The flash fire engulfed the gaming hall, trapping patrons scrambling for the few exits and hiding in bathrooms. The toll was among the highest for a single attack since a government crackdown on organized crime began in 2006 and infighting among gangs unleashed an explosion of violence that has left more than 35,000 dead.

Although no motive has been determined, it bore the hallmarks of an organized crime assault, and government officials and security analysts said the brutality suggested the work of the Zetas, one of the largest and most feared gangs in the area.