(CNN) Only the shallow waters of the Rio Grande and a couple of miles separated Mexican drug kingpin Joaquin "El Chapo" Guzman from American soil Saturday.

Guzman was transferred from the maximum-security Altiplano lockup in central Mexico to a prison in Ciudad Juarez, a senior Mexican law enforcement source told CNN.

"Due to the proximity (to the U.S.), it makes it easier to extradite him," the official said.

The exact reason for the move is unclear, but it comes one month after a Mexican lawyer leading his legal defense team said his client wanted to be extradited to the United States "as soon as possible" because conditions at Altiplano were unbearable and making him seriously ill.

Altiplano is the same lockup near Mexico City from which the drug lord escaped last July and to which he was returned after his January 8 recapture in the coastal city of Los Mochis in Sinaloa state. "El Chapo" slipped out through a prison tunnel in the brazen escape, taking advantage of a blind spot in a cell security camera.

Now the notorious Sinaloa cartel boss finds himself behind bars just across from El Paso, Texas.

Photos: 'El Chapo' in prison Photos: 'El Chapo' in prison Joaquin "El Chapo" Guzman stands in his cell at the Altiplano Federal Prison in Mexico. Increased security measures are being used by authorities to make sure the cartel kingpin doesn't break out of prison for a third time. His most recent escape came in July, when he got out through a hole in the floor of his cell's shower stall. The images in this gallery were obtained by Mexican journalist Carlos Loret de Mola. Hide Caption 1 of 7 Photos: 'El Chapo' in prison Military vehicles and canine officers guard the Altiplano prison. Hide Caption 2 of 7 Photos: 'El Chapo' in prison Guards walk down a hallway of the prison, which has installed 400 new cameras. Authorities hope to add another 600 by April. Hide Caption 3 of 7 Photos: 'El Chapo' in prison An X-ray machine is guarded at the prison's entrance.

Hide Caption 4 of 7 Photos: 'El Chapo' in prison A body scan machine is also at the front entrance. Hide Caption 5 of 7 Photos: 'El Chapo' in prison An officer operates the body scan machine. Hide Caption 6 of 7 Photos: 'El Chapo' in prison An officer at the entrance swabs a visitor to detect explosives. Hide Caption 7 of 7

In a statement, Mexico's National Safety Commission said Guzman was transferred to the "CEFERESO No. 9" facility in the northern state of Chihuahua.

"Such transfer was carried out with full respect for the human rights of the inmate," the statement said.

Preparations for extradition?

Mexico's government attributed Guzman's transfer to renovations intended to improve security at Altiplano.

But the United States has been preparing for Guzman's transfer for months and have been hammering out the security details, American officials said.

It's not immediately clear when Guzman will be turned over to U.S. custody.

Once he is transferred, Guzman will be sent to Brooklyn, New York, to stand trial on federal charges, the officials told CNN.

Jose Refugio Rodriguez, Guzman's lead attorney, confirmed the transfer. He said lawyers were not notified and their client may have learned of the transfer at the last minute.

Rodriguez said his client's extradition is not imminent and will not occur "for some time." Another member of Guzman's legal team, Andres Granado, was flying to Juarez to meet with Guzman, according to Rodriguez.

In recent weeks, Justice Department officials held a conference call with several federal prosecutors handling pending cases against Guzman.

Top Justice Department officials decided a case largely based on a Homeland Security Department investigation would be the charges for which he would stand trial.

The Brooklyn venue offers advantages because a federal detention center that is part of the court complex offers the appropriate level of security, according to the officials.

In Brooklyn, Guzman and other cartel leaders were indicted in 2009 on charges of conspiring to import more than 264,000 pounds of cocaine into the United States between 1990 and 2005, according to the U.S. Justice Department. The traffickers also are accused of sharing drug transportation routes and obtaining their drugs from various Colombian drug organizations.

The indictments allege Guzman and others cartel bosses employed "sicarios," or hit men, to carry out hundreds of acts of violence in Mexico, including murders, kidnappings, tortures and violent collections of drug debts, according to federal prosecutors.

Rodriguez told CNN in early March that Guzman would be willing to plead guilty on drug trafficking charges in the United States as long as he's held at a medium-security prison, allowed to see family members and his attorney often, and is not kept in isolation.

But the attorney changed his tune in a separate CNN interview last month, saying Guzman's request to be extradited was merely a tactic in response to the poor treatment his client was receiving in a Mexican prison.

Photos: Joaquin 'El Chapo' Guzman's 2015 escape Photos: Joaquin 'El Chapo' Guzman's 2015 escape Joaquin "El Chapo" Guzman was considered the world's most powerful drug lord until his arrest in Mexico in February 2014. He escaped from a maximum-security prison on July 11, 2015. Hide Caption 1 of 6 Photos: Joaquin 'El Chapo' Guzman's 2015 escape This screen grab of security video, dated July 11 and released by Mexico's National Security Commission, shows Guzman inside his cell at the Altiplano prison in Almoloya de Juarez, Mexico. He is looking at the shower floor shortly before escaping through a tunnel below, authorities said. Hide Caption 2 of 6 Photos: Joaquin 'El Chapo' Guzman's 2015 escape A journalist climbs a ladder to get out of the tunnel that authorities say Guzman used to escape. Hide Caption 3 of 6 Photos: Joaquin 'El Chapo' Guzman's 2015 escape Journalists exit the tunnel on Tuesday, July 14. Hide Caption 4 of 6 Photos: Joaquin 'El Chapo' Guzman's 2015 escape Yellow police tape surrounds the construction site where the exit of the tunnel is located. Hide Caption 5 of 6 Photos: Joaquin 'El Chapo' Guzman's 2015 escape Federal police guard a drainage pipe outside of the prison on Sunday, July 12. Hide Caption 6 of 6

Guzman is the focus of 10 legal cases in Mexico, mainly for drug trafficking, murder and charges related to his role as a cartel leader. But he also faces charges in Arizona, California, Texas, Illinois, New York, Florida and New Hampshire.

Guzman and his lieutenants are named in U.S. indictments for alleged involvement in marijuana, cocaine and heroin trafficking, as well as racketeering, money laundering, kidnapping and conspiracy to commit murder.

Altiplano is the same prison near Mexico City from which the drug lord escaped last July and to which he was returned after his January 8 recapture in the coastal city of Los Mochis in Sinaloa state.

President Enrique Peña Nieto said in late January that he's directed his attorney general's office to "make this extradition of this highly dangerous criminal happen as soon as possible." Mexico began proceedings for the extradition that same month.

Why hasn't he been sent to U.S.?

In the past, Mexican authorities asserted their sovereignty to first prosecute Guzman for crimes in Mexico, despite U.S. officials' concerns the drug kingpin would escape from prison as he had done in 2001.

Analysts have advanced various theories on why Mexico declined to extradite Guzman to the United States shortly after his arrest in 2014.

Some said Nieto wanted to limit U.S. involvement in Mexico's drug war and felt having the United States possibly imprison Mexico's top criminal would be a blow to the country's ego and sovereignty.

Others offered that Mexican officials feared Guzman might expose dirty dealings with the country's politicians. And former Attorney General Jesus Murillo Karam said he disapproved of the United States cutting deals with criminals -- as it did in 2013 with Jesús Vicente "El Vicentillo" Zambada Niebla, the son of Guzman's top lieutenant -- and not sharing with Mexico any intelligence from their cooperation.

Officially, Murillo Karam said Guzman would not be extradited until he finished serving his time in Mexico, a sentiment echoed by the ambassador to the United States, Eduardo Medina-Mora. When Guzman escaped in 2001, he had served seven years of a more than 20-year sentence, and he racked up eight more charges before being recaptured.

Guzman -- whose nickname means "Shorty" for his 5-foot-6-inch frame -- infamously escaped in 2001 from a high-security prison in a laundry cart. He avoided capture through the years due to his enormous power to bribe corrupt local, state and federal Mexican officials.

His drug enterprise stretches throughout North America and reaches as far away as Europe and Australia.

The Sinaloa cartel has been blamed for its role in the bloody drug war that has plagued Mexico in recent years, leaving tens of thousands of people dead.