CHICAGO — Mexican drug cartels whose operatives once rarely ventured beyond the U.S. border are dispatching some of their most trusted agents to live and work deep inside the United States — an emboldened presence that experts said they believe is meant to tighten their grip on the world’s most lucrative narcotics market and maximize profits.

Cartel activity in the U.S. is certainly not new. Starting in the 1990s, the ruthless syndicates became the nation’s No. 1 supplier of illegal drugs, using unaffiliated middlemen to smuggle cocaine, marijuana and heroin beyond the border or even to grow pot here.

But a wide-ranging Associated Press review of federal court cases and government drug-enforcement data, plus interviews with many top law enforcement officials, indicate the groups have begun deploying agents from their inner circles to the U.S. Cartel operatives are suspected of running drug-distribution networks in at least nine non-border states, often in middle-class suburbs in the Midwest, South and Northeast.

Border states from Texas to California have long grappled with a cartel presence, but cases involving cartel members have now emerged in the suburbs of Chicago and Atlanta, as well as Columbus, Ohio, Louisville, Ky., and rural North Carolina. Suspects have also surfaced in Indiana, Michigan, Minnesota and Pennsylvania.

Mexican drug cartels “are taking over our neighborhoods,” Pennsylvania Attorney General Kathleen Kane warned a legislative committee in February. State Police Commissioner Frank Noonan disputed her claim, saying cartels are primarily drug suppliers, not the ones trafficking drugs on the ground.

Others are skeptical about claims cartels are expanding their presence, saying law-enforcement agencies are prone to exaggerating threats to justify bigger budgets. An Atlanta attorney who has represented reputed cartel members said authorities sometimes overstate the threat such men pose.

“Often, you have a kid whose first time leaving Mexico is sleeping on a mattress at a stash house playing Game Boy, eating Burger King, just checking drugs or money in and out,” said Bruce Harvey. “Then he’s arrested and gets a gargantuan sentence. It’s sad.”