Mexico has transferred the convicted drug lord, Joaquin Guzman, to a prison close to the border with the US.
Known as "El Chapo", he was taken to a prison near Ciudad Juarez, across the border from El Paso in Texas, as part of a normal rotation of prisoners for security reasons, officials said.
The head of the Sinaloa drug cartel, Guzman was re-captured in January, six months after he escaped from prison.
Guzman is wanted in the US on charges of smuggling drugs into the country.
Mexican officials told Reuters news agency that Guzman's transfer to Ciudad Juarez was not a precursor to extradition.
Mexico's National Security Commission said it was in line with security protocols, and it had rotated more than 7,400 inmates as part of new security strategy.
The authorities said that Guzman was moved to a new prison "because of works taking place to reinforce security" in Altiplano - his old prison near Mexico City.
Analysts suggested the move was to prevent him escaping during the works.
Guzman, who was named Public Enemy Number One by the Chicago Crime Commission in 2013, has been indicted by at least seven US federal district courts.
Mexican officials say the process to extradite him to the US could take at least a year.
In March, Guzman asked to be extradited rapidly so he could receive better treatment in prison.
His lawyer said Guzman had asked him to stop fighting his extradition because guards at his prison would not let him sleep.
Guzman was captured in January and returned to the Altiplano maximum security jail near Mexico City after six months on the run.
He had escaped from Altiplano in July through a 1.5km-long (one mile) tunnel under the floor of his shower stall in his cell.
Leaked security footage of Guzman's prison break showed how guards failed to detect his escape until more than 20 minutes after it had happened, despite the sound of loud banging coming from his cell.
Mexican marines arrested him in the western state of Sinaloa after he fled a safe house through a storm drain.
The prison director and a number of guards were arrested in connection with his escape.
February 2014: Recapture after 13 years on the run following "laundry basket" escape from Puente Grande maximum security prison
July 2015: Escape via tunnel from Altiplano prison
2 October 2015: Interviewed by US actor Sean Penn in Durango state jungle hideout and then by phone and video
17 October: Mexican officials announce narrow escape as police try to recapture him in neighbouring Sinaloa state
January 2016: Recaptured in Los Mochis, Sinaloa state