The attorney general's office said it would take no action against retired general Salvador Cienfuegos, whose surprise arrest at a Los Angeles airport in October had sparked diplomatic tensions.

The office said that it had concluded that Cienfuegos "never had any meeting with the members of the criminal organization investigated by the US authorities.

"He did not have any communication with them, nor did he carry out acts intended to protect or help those individuals," it added.

Salvador Cienfuegos was accused by the US of conspiring to produce and distribute "thousands of kilograms" of cocaine, heroin, methamphetamine and marijuana.

The retired general, nicknamed "The Godfather," had faced a possible life sentence in the US if convicted of the drug trafficking and money laundering charges, which he denied.

After diplomatic pressure from Mexico, US authorities dropped the charges and sent Cienfuegos home for possible prosecution.

The indictment of Cienfuegos, a key figure in ex-president Enrique Pena Nieto's 2012 to 2018 government, surprised and irritated Mexican officials.

It triggered a diplomatic row that experts said could have jeopardized the countries' cooperation in fighting powerful cartels.

Experts had said after Cienfuegos was sent home that political interests and the military's power made it unlikely that he would ever stand trial in Mexico.