WASHINGTON—The Defense Department said Wednesday that it had transferred a prisoner from Guantanamo Bay to Saudi Arabia, the first such detainee transfer to take place under President Donald Trump.
The Pentagon separately said it had issued new guidelines for transferring new detainees to the military facility, which is part of a U.S. naval base in Cuba. It didn’t say how the updated policy would affect enemy combatants currently held abroad.
In January, Mr. Trump signed an executive order to keep Guantanamo Bay operating, reversing a 2009 order by his predecessor to close the facility. Its operating costs are about $400 million a year. Mr. Trump said at the time that keeping it open would prevent the release of suspected terrorists back to the battlefield.
The Pentagon said that it had transferred Guantanamo detainee Ahmed Mohammed Ahmed Haza al-Darbi to Saudi Arabia, his native country. In 2014, Mr. Darbi pleaded guilty to various offenses, including an attempt to attack shipping vessels in the Strait of Hormuz. The Pentagon said he would serve the remainder of his 13-year sentence in Saudi Arabia.
The transfer reduced the detainee population at Guantanamo Bay to 40 individuals.
Mr. Trump has previously criticized his predecessor’s efforts to close the facility. “There should be no further releases from Gitmo. These are extremely dangerous people and should not be allowed back onto the battlefield,” Mr. Trump wrote in a tweet in January 2017.
The Pentagon declined to comment on how the new guidelines might apply to new prisoners captured in the fight against Islamic State, such as a U.S.-Saudi dual citizen held at a secret military facility in Iraq.
“This policy provides our warfighters guidance on nominating detainees for transfer to Guantanamo detention should that person present a continuing, significant threat to the security of the United States,” said Cmdr. Sarah Higgins, a spokeswoman for the Pentagon.
The Justice Department also declined to comment on the U.S.-Saudi dual citizen’s case, which has been in limbo since a federal judge blocked the suspect’s transfer to Saudi Arabia last month.
Rights groups criticized the Pentagon’s decision to issue secret guidelines and continued to advocate the closure of the facility.
“Although so far the new policy is secret, the government’s statement suggests it will allow new detainees to be transferred to Guantanamo,” said Daphne Eviatar of Amnesty International USA. “Given the history of torture, unlawful detention and complete lack of justice provided there, no new detainees should ever be transferred to Guantanamo.”
Since Sept. 11, 2001, 779 men have been held at Guantanamo, the State Department has said. The administration of President George W. Bush released 532 and Mr. Obama’s released 197. Nine prisoners died while in custody.
Mr. Darbi, the latest prisoner to be transferred, pleaded guilty to charges stemming from a 2002 terrorist attack on a French oil tanker that left one civilian crew member dead. The plea bargain calls for another five to 11 years’ incarceration in Saudi Arabia following Mr. Darbi’s repatriation.
A spokeswoman for the Saudi embassy didn’t immediately respond to a request to comment on whether Mr. Darbi, who has been detained by the U.S. military since 2002, will continue to be jailed there.
U.S. investigators have concluded that Mr. Darbi was abused by interrogators during the early years of his detention.
Mr. Trump had long expressed skepticism of Mr. Obama’s efforts to close the detention center, and on the campaign trail Mr. Trump referred to Guantanamo Bay by pledging to “load it up with some bad dudes.”
But State Department and Pentagon officials said earlier this year there were no plans to send new detainees to Guantanamo. No detainee has been sent to Guantanamo in nearly a decade.
—Gordon Lubold and Jess Bravin contributed to this article.