"It's a very regrettable fact that a former defense minister is arrested, accused of links with drug trafficking," said Lopez Obrador told reporters a day after Cienfuegos was detained at Los Angeles airport.

"Of course, all this must be proven," he said, adding that the US authorities were expected to announce the reasons for the arrest later Friday.

The 72-year-old general, who was defense chief from 2012 to 2018 under former president Enrique Pena Nieto, is reported to have been on a trip with his family when he was detained.

"We are facing an unprecedented situation" Lopez Obrador said, noting that two former Mexican ministers are now detained in the US on allegations of links to drug cartels.

Ex-public security minister Genaro Garcia Luna was arrested in Texas in December 2019 on charges of taking huge bribes to allow the notorious Sinaloa cartel to ship drugs into the US.