Former Coahuila governor Humberto Moreira, whose son was allegedly killed by the Zetas drug cartel, has charged that some mine businessmen have bought coal from organized crime and sold it to the state-run power company CFE.

Interior Minister Alejandro Poire told a news conference that investigations into such allegations began months ago.

"There are joint state and federal government investigations regarding this matter to verify if these allegations about the participation of other agents are valid or not," Poire said.

The newspaper Reforma reported that the federal prosecutor's office is probing three companies over their alleged links to illegal activities in Coahuila, which is home to 95 percent of Mexico's coal reserves.

The daily, citing unnamed officials, said the Zetas have sold coal to companies at below-market prices as a way to launder money.

Moreira, who was governor from 2005 to 2011, has accused the Zetas of assassinating his 25-year-old son Jose Eduardo in early October to avenge the killing a cartel leader's nephew by state authorities.