A witness at the US trial of Joaquín “El Chapo” Guzmán has testified that he told US authorities the accused Mexican drug lord once paid a $100m bribe to the former Mexican president Enrique Peña Nieto.

Alex Cifuentes, who has said he was a close associate of the Sinaloa cartel chief for years, discussed the alleged bribe under cross-examination by one of Guzmán’s lawyers in Brooklyn federal court on Tuesday. Asked if he told authorities in 2016 that Guzmán arranged the bribe, he answered: “That’s right.”

Peña Nieto was president of Mexico from December 2012 until November 2018. He previously served as governor of the state of Mexico.

The former president made no immediate comment on the allegation. His former chief of staff, however, took to social media to reject the accusation.

“The declarations of the Colombian drug trafficker in New York are false, defamatory and absurd,” tweeted Francisco Guzmán, adding that the Peña Nieto government “located, detained and extradited” the Mexican kingpin.

The allegations are among the most explosive to emerge from Guzmán’s trial, which began in November and has so far featured testimony of lower-level corruption.

Guzmán, 61, was extradited to the US in 2017 to face charges of trafficking cocaine, heroin and other drugs into the country as leader of the Sinaloa cartel.

At the start of the trial in November, defence attorney Jeffrey Lichtman alleged on behalf of his client that that Mexican officials – including Peña Nieto and his predecessor – had received bribes to protect Ismael “El Mayo” Zambada, another reputed trafficker who is still at large.

At the time, a spokesman for Peña Nieto called the allegation “false and defamatory”, while his predecessor Felipe Calderón tweeted that the remarks were “absolutely false and reckless”.

The judge in the case, Brian Cogan admonished Lichtman for having gone “far afield of direct or circumstantial proof”. He said he would instruct the jury to focus on the evidence.

At the end of the first week of trial, Guzmán’s lawyers told the judge that a witness would describe a payment to an “incumbent” Mexican president.

He was stopped from doing so by a prosecutors’ motion, upheld by Judge Cogan, “protecting individuals and entities who are not parties to this case and who would face embarrassment”.