The smuggling of Cuban immigrants through Mexico's Yucatan Peninsula - illegal trade that is exited by the U.S. policy of granting Cubans automatic asylum.
A violent ring of immigrant smugglers operates in Mexico, where Cubans land on the coasts in rickety boats before crossing overland to the U.S. border, Medina Mora told reporters.
"This has been legally proved, that people of Cuban origin but who are citizens of the United States are involved, financing these people-smuggling operations, obviously with the complicity of Mexicans," the attorney general said.
"This has to do with U.S. policy toward Cubans," he said. "Those who make it to (U.S.) territory by their own means can get automatic refugee status, so that policy serves as an incentive" to smuggle Cubans here.
Under the so-called "wet foot, dry foot" policy, the U.S. turns back Cubans intercepted on the seas but grants asylum to most who make it to shore. To avoid capture by U.S. authorities before making it to land, many Cubans decide to go through Mexico.
Mexico is struggling to deal with a series of gangland-style slayings apparently related to the trafficking of migrants from Cuba, which lies only about 130 miles (210 kilometers) east of the Yucatan Peninsula, just slightly farther by boat from Cuba than Florida.
In a new trend, nearly 90 percent of all undocumented Cubans who make it to the United States now travel overland rather than reaching U.S. shores by boat, according to the U.S. Customs and Border Protection.
Mexico also is having problems with its burgeoning population of detained Cuban migrants, most of whom want to go to the U.S. Most Cubans are released after being held 90 days at a Mexican immigration center. Only about one-third of all those arrested in 2006 were repatriated to Cuba, Mexican migration officials say.
Last week, three Cuban immigrants were treated for dehydration at a Mexican hospital after going on a hunger strike to demand release from a detention center. They were returned to the center and are awaiting decisions in their cases.