(Reuters) - Held without access to sunlight or his relatives, Mexican drug lord Joaquin “El Chapo” Guzman is under more restrictive captivity than any other U.S. prisoner and it is difficult to mount a defense, his court-appointed lawyers said on Thursday.

FILE PHOTO: Mexico's top drug lord Joaquin "El Chapo" Guzman is escorted as he arrives at Long Island MacArthur airport in New York, U.S., January 19, 2017, after his extradition from Mexico. U.S. officials/Handout via REUTERS

Mexico extradited Guzman, who is the head of Sinaloa Cartel, to New York in January, a few hours before U.S. President Donald Trump took office. Guzman, who escaped from two Mexican prisons and was a key figure in a bloody drug war, is seen as a flight risk by the U.S. government.

Guzman is restricted to his New York City cell for 23 hours a day, with the lights on at all times. He has one hour of exercise in a small interior cage with no access to fresh air or sunlight, Amnesty International said in a letter to Assistant U.S. Attorney Andrea Goldbarg dated March 28.

Saying that Guzman’s captivity appeared to be “unnecessarily harsh” and in contravention of minimum U.N. standards for the treatment of prisoners, the human rights group has requested access to his cell to verify the conditions.

“We will continue to investigate cases of alleged improper treatment of prisoners, regardless of who the prisoner is or what they may have done,” Amnesty International’s Americas Director Erika Guevera-Rosas said in a statement.

Guzman, who sold oranges as a child before turning to the drug trade in the 1970s, has not been allowed to speak to his wife or other family members. The conditions of captivity exceed any other mainland U.S. prison, including the super-secure Colorado prison known as Supermax, public defense attorney Michelle Gelernt said.

“Mr. Guzman is being held under the worst, most restrictive conditions of any prisoner currently detained by the United States government,” Gelernt said.”Even convicted prisoners held in the notorious federal Supermax in Colorado are allowed to watch television in their cells, exercise outside where they can speak with other inmates, and speak with their families. Mr. Guzman enjoys none of these benefits.”

The U.S. confinement conditions, especially restrictions on communicating with family members, mean it is tough for Guzman to contact private lawyers because he is not able to speak to his family to arrange payment or discuss potential attorneys, Gelernt said.

“The need to continually seek relief from the draconian jail conditions will distract Mr. Guzman and his lawyers from defending against the charges,” she said.

In a filing on Wednesday to U.S. District Judge Brian Cogan of the Eastern District of New York, Guzman’s lawyers said the strict confinement puts Guzman at risk of psychological damage, and that he may already be “hearing non-existent sounds.”

U.S. prosecutors have argued that such tough measures - called Special Administrative Measures - are needed to prevent Guzman from communicating with his cartel cohorts still running the multinational trafficking organization, and to prevent repeats of his two Mexican prison escapes.

In his most recent escape in 2015, Guzman walked out of prison through a mile-long highly engineered tunnel from his cell, a sign of the huge influence he was able to wield even from behind bars.