By Matt Spetalnick

WASHINGTON (Reuters) - A Mauritanian prisoner who wrote a best-selling memoir about his long ordeal at the U.S. military prison at Guantanamo has been cleared for release, his lawyers and a U.S. official said on Wednesday.

A parole-style review opened the way for Mohamedou Ould Slahi, author of “Guantanamo Diary,” to be moved out of the detention center at the U.S. naval base in Cuba. But he cannot leave until U.S. authorities make arrangements for him to be repatriated to his West African homeland or to send him to another country.

Slahi, 45, who arrived in Guantanamo in August 2002 and has been held without charge or trial, appeared before a Periodic Review Board – a multi-agency government panel – on June 2.

His hearing was part of President Barack Obama's stepped-up effort to whittle down the Guantanamo inmate population to meet his promise to close the prison by the end of his tenure in January, a prospect that looks increasingly doubtful due to U.S. congressional opposition. The latest decision means that 30 of the 76 detainees are now cleared for release.

Slahi became one of Guantanamo's most prominent inmates with the 2015 publication of his prison memoir in which he described his years of detention and interrogation, including being subjected to harsh techniques widely considered torture. U.S. censors heavily redacted the 466-page manuscript he gave to his lawyers.

Slahi was first detained by authorities in Mauritania and was then sent to Jordan and Afghanistan and finally to the Guantanamo prison, which was opened under President George W. Bush to hold terrorism suspects rounded up overseas following the Sept. 11, 2001 attacks. The facility became a symbol of the excesses of Bush’s “war on terror.”

Slahi was originally suspected of being a senior recruiter for al Qaeda. But his lawyers contended that his links to militants had been limited to the early 1990s when he fought in Afghanistan with the mujahideen anti-communist insurgents.

The review board determined that Slahi "poses no significant threat to the United States," the American Civil Liberties Union said. A U.S. official, speaking on condition of anonymity, confirmed Slahi was cleared for release and the ruling would soon be officially released.

“We will now work toward his quick release and return to the waiting arms of his loving family," said Nancy Hollander, one of Slahi’s attorneys, in a statement issued by the ACLU.

The timing of Slahi’s departure could depend on whether he can return to Mauritania. Many cleared prisoners have been held for years while the U.S. government seeks a country to accept them.

(Reporting By Matt Spetalnick; Editing by Chris Reese)