Mexican President Andres Manuel Lopez Obrador on Monday denied that Mexico had agreed to capture a cartel leader for the United States in order to secure the return of ex-defense minister Salvador Cienfuegos from U.S. custody.

Reuters reported last week that Mexico agreed with U.S. Attorney General William Barr to seek the arrest of a high-level Mexican drug cartel leader as part of a deal to get U.S. drug trafficking charges against Cienfuegos dropped.

"There is no deal in the shadows," Lopez Obrador said at his regular news conference, referring to the Reuters story as well as other media reports that Mexico had threatened to expel U.S. Drug Enforcement Administration agents over Cienfuegos' arrest.

He said it was wrong to suggest that the United States sent Cienfuegos back so that Mexico would send Washington a leader of organized crime.

Cienfuegos' arrest in Los Angeles in October followed a multi-year investigation that used wire taps to track a military figure, dubbed "El Padrino" (The Godfather) by traffickers.

Investigators concluded "El Padrino" was Cienfuegos and that he helped drug traffickers move tonnes of narcotics.

Mexico's government, angry it was not forewarned about the investigation, hailed Cienfuegos' return on Wednesday as a diplomatic achievement and a win for the nation's sovereignty.