MEXICO CITY • The Mexican authorities yesterday formally launched the process to extradite drug lord Joaquin "El Chapo" Guzman to the United States, as they also sought to question actor Sean Penn over their secret meeting.

The extradition bid marks a reversal from President Enrique Pena Nieto's refusal to send Guzman across the border prior to his July escape from a maximum-security prison.

Agents from Interpol Mexico went to Guzman's prison near Mexico City to execute two arrest warrants for his extradition, two days after he was captured in a deadly military raid. Mexico received the US extradition requests last year on a slew of charges, including drug trafficking and homicide.

The narcotics kingpin is wanted in a half-dozen US states and the possibility of extradition sets up the prospect of one of the biggest federal trials in the US in recent years.

A Mexican official told AFP the process could take "months", but that the authorities will likely "try to do it fast".

After judges rule on the extradition, the foreign ministry has to issue a decision, which Guzman can appeal against.

His attorney has vowed a "tough" legal fight that could reach the Supreme Court.

Meanwhile, the Mexican authorities said they want to question Penn over his October meeting with the then fugitive.

A Mexican federal official told AFP that the Attorney-General's Office also wants to speak to Mexican actress Kate del Castillo, who brokered the meeting.

"That is correct, it's to determine responsibilities," the official said, while declining to provide details, including a possible date for an interview with the actors.

AGENCE FRANCE PRESSE, NEW YORK TIMES