Flowers are placed to mourn the victims of the 9/11 terror attacks at the National September 11 Memorial and Museum in New York, the United States, September 11, 2019.Photo: Xinhua

A man accused of being the would-be 20th hijacker in the September 11, 2001 attacks has been repatriated to Saudi Arabia after two decades detained at Guantanamo Bay, the US Department of Defense said on Monday.

Mohammad Mani Ahmad al-Qahtani, 46, was transferred to his native Saudi Arabia after a review board determined in June that he no longer represented a significant threat to US national security, the Defense Department said in a written statement.

"The United States appreciates the willingness of Saudi Arabia and other partners to support ongoing US efforts toward a deliberate and thorough process focused on responsibly reducing the detainee population and ultimately closing of the Guantanamo Bay facility," the statement said.

According to a Guantanamo detainee profile maintained by the Defense Department, al-Qahtani was trained by al-Quaeda and sought unsuccessfully to enter the US on August 4, 2001 to take part in the September 11 attacks.

In all, 38 detainees remain at Guantanamo Bay. Of those, 19 are eligible for transfer, seven are eligible for a Periodic Review Board, 10 are involved in the military commissions process and two detainees have been convicted in military commissions.

Reuters