A longtime Guantanamo Bay prisoner who wrote a best-selling book about his experiences in the controversial military prison was back in his native Mauritania on Monday night, Mauritanian sources said.

The transfer of Mohamedou Ould Slahi, believed to be the last inmate from Mauritania held at the facility in Cuba, brings the prison's remaining population down to 60.

His case became a cause celebre after the publication last year of "Guantanamo Diary", in which he outlines his treatment at the notorious US naval base in Cuba and says he was subjected to torture.

Mauritania's official AMI news agency confirmed "the return by the American authorities to their Mauritanian counterparts Mohamedou Ould Sellahy (or Slahi) after his release from Guantanamo."

AMI said the handover was the result of "diplomatic efforts over many years at the highest levels."

The US Defense Department announced his release in an earlier statement and said it was "grateful to the government of Mauritania for its humanitarian gesture and willingness to support ongoing US efforts to close the Guantanamo Bay detention facility."

Slahi, 45, was detained in his home country following the September 11 attacks on the United States in 2001, on suspicion of involvement in an unsuccessful plot to bomb Los Angeles in 1999.

He was taken to Guantanamo in August 2002 following interrogation in Jordan and Afghanistan.

In his book, Slahi described the toll of life inside the jail, saying: "I started to hallucinate and hear voices as clear as crystal. I heard my family in a casual familial conversation ... I heard Koran readings in a heavenly voice."

He added: "I was on the edge of losing my mind."

A Mauritanian security source told AFP Slahi had arrived in the capital Nouakchott on Monday in a US military plane, and was met by the Mauritanian security services.

"He will not be free to move around immediately but has to be interviewed by the security services before being released," the source said.

US President Barack Obama wants to close the Guantanamo jail before he leaves office, but his efforts have faced stiff Republican opposition and time to shutter the prison is running out fast.

Still, the United States has in recent months accelerated the rate at which detainees who have been approved for transfer are released from the facility.
When Obama took office, there were 242 detainees at Guantanamo.