Mohamedou Ould Slahi, the author of an internationally bestselling memoir that detailed the torture he endured as a detainee in Guantánamo Bay, says he has been denied a passport by Mauritania, the country of his birth, three years after he was released from the US detention centre.

The writer is petitioning Mauritania’s minister of the interior, Ahmedou Ould-Abdallah, over the denial of a passport. He had been told by the government he would be eligible to travel again two years after being released from Guantánamo. Slahi is supported by almost 200 writers, editors, publishers, teachers and human-rights advocates, who have written to Ould-Abdallah describing the rejection as “extrajudicial punishment of a man who has never engaged in terrorism nor ever been charged with or convicted of a crime”.

Slahi was held at Guantánamo without charge between August 2002 and October 2016. He had fought alongside men who would join al-Qaida in the Afghanistan insurrection, but says he renounced the group in the 1990s. He turned himself in for questioning in Mauritania after the 9/11 attacks, and was subsequently rendered to Jordan, Afghanistan and then to Guantánamo Bay. His memoir about that time, Guantánamo Diary, details the torture he underwent, including isolation, beatings, sexual humiliation, death threats, and a mock kidnapping. It has been published in 29 countries and 26 languages, and was longlisted for the UK’s leading non-fiction award, the Samuel Johnson prize.

Slahi was released in 2016 after 14 years in the detention centre, and transferred to Mauritania.

“When I came they told me the United States asked us not to give you a passport back, to ban you from travelling for two years. I told the guy who told me that I completely and utterly reject that. I’m not a convicted felon. But I didn’t do any legal stuff [then],” he told the Guardian, describing the situation as extremely frustrating.

The rejection of his recent application, however, prompted him to go public. The petition and attached letter of support is “a warning to the government. If you don’t give me my papers, I’m going to court,” he said. “They were very clear about it. They said the United States government asked them not to. I go to the United States, they said: ‘You are not a citizen, you are not in Guantánamo Bay. It is up to your country.’”

The Mauritanian embassy in London did not respond to a request for comment.

“It just demonstrates how arbitrary and absurd the restrictions are,” said Larry Siems, the author and human rights advocate who edited Guantánamo Diary. “People who know him best and know his situation understand how grossly unjust it is that he continues to be punished for nothing, and the international support from the letter shows he is reaching people … He appears frequently for classroom discussions by Skype around the world. He’s reached hearts and minds of students and faculty around the world. We live in this globalised world and those exchanges have all been incredibly positive, and there’s no reason to try to interrupt or impede them.”

The letter describes the urgency of Slahi’s need for a passport, with doctors in Mauritania, the US and Germany stating that Slahi “requires advanced medical treatment for conditions associated with his ordeal of detention and abuse”, with one German doctor willing to “oversee and cover all costs associated with his treatment”.

Slahi’s supporters in the petition described him as “an important international voice for justice, peace, reconciliation and faith” despite “the litany of injustices and human rights abuses” he has endured.

The letter adds: “It is time to restore his freedom to travel so that he may enjoy his rights as a Mauritanian and fully represent his country and his values to the world … He is not just an important literary voice; he is also an inspirational public figure who projects the essential human values of dignity, grace, peace, family, tolerance, faith and community. Authorising Mr Slahi’s freedom to travel will facilitate mutual respect and understanding across cultures, and enhance international appreciation of your country and its rich cultural heritage.”

Slahi said that he has “so many people supporting me, but none of them can make decisions … It’s very dangerous. I’m exposed, very exposed.”