NEW YORK (Reuters) - A witness at the U.S. drug trafficking trial of accused Sinaloa Cartel leader Joaquin “El Chapo” Guzman on Tuesday testified that he paid a multimillion-dollar bribe to an underling of Mexican President-elect Andres Manuel Lopez Obrador in 2005.

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The witness, Jesus Zambada, also said he paid millions of dollars in bribes to former Mexican government official Genaro Garcia Luna on behalf of his brother, drug lord Ismael “El Mayo” Zambada, who remains at large.

A spokesman for Lopez Obrador did not immediately respond to a call and text message seeking comment.

Garcia Luna, in a written statement, said the accusations were “defamation” and “perjury” and made without any proof.

Garcia Luna said he had received commendations from high-level U.S. officials for his labors in fighting organized crime in Mexico and that he had been “systematically defamed” due to the actions he took against criminal networks.

“There has never been a single proof or evidence of all those infamies,” he said.

Zambada gave his testimony about the bribes on the fifth day of trial under cross-examination by one of Guzman’s lawyers, William Purpura. Guzman’s lawyers have said they will try to prove that Guzman is being scapegoated and that Ismael Zambada was the real head of the Sinaloa Cartel.

Guzman, 61, is charged with 17 criminal counts and faces life in prison if he is convicted. He was extradited to the United States in January 2017, after twice escaping Mexican prisons.

Zambada, who was called to testify against Guzman under an agreement with U.S. prosecutors, previously told jurors that his brother and Guzman worked together for years to move multi-ton shipments of cocaine from Colombia through Mexico into the United States, while arranging for their rivals to be murdered.

During Purpura’s cross-examination, Zambada said he paid “a few million” dollars to a Mexico City government official while Lopez Obrador was head of government there. He said the bribe was paid because it was believed at the time that the official could become Mexico’s next secretary of public security.

The name of the official was not immediately clear from the court testimony. But Gabriel Regino, a former subsecretary of public security in Mexico City who is now a criminal law professor at the National Autonomous University of Mexico, wrote on Twitter that an accusation of bribery had emerged against him in the trial but was false.

Zambada also said under cross-examination that he handed a suitcase containing $3 million to Garcia Luna in 2005 or 2006, when Garcia Luna was director of Mexico’s Federal Investigation Agency.

Garcia Luna said the charge was “unbelievable” since he was not able to appoint officials to posts, as Zambada alleged, and such designations were made by a council.

Zamabda said he gave him another $3 million to $5 million in 2007, when he had become secretary of public security, to secure favorable treatment for the cartel.

Garcia Luna said he never had contact with Zambada and there was a public record of all his meetings in and out of the office when he was secretary of public security.