A federal judge in Washington blocked the Pentagon from transferring a Guantanamo Bay detainee to Tunisia, where he allegedly faces torture, according to a ruling unsealed Tuesday that marked a milestone in the treatment of detainees.

The order by U.S. District Judge Gladys Kessler was unprecedented as a direct intervention in the case of a prisoner at Guantanamo Bay, where some 330 men accused of links to Al Qaeda or the Taliban are held, the detainee's lawyers said.

"It's the first time the judiciary has given a detainee any substantive right — in this case it is the right not to be tortured by the Tunisian government," said Joshua Denbeaux, the lawyer for Mohammed Abdul Rahman, the Tunisian detainee.

Kessler said that Rahman, who has a heart condition, was convicted in absentia in Tunisia, sentenced to 20 years in prison and allegedly would face torture there, demonstrating "the devastating and irreparable harm he is likely to face if transferred."

In the Oct. 2 ruling kept under seal until Tuesday, Kessler granted a preliminary injunction to halt the Defense Department's move to transfer Rahman to Tunisia. He was captured in Pakistan and allegedly handed over for a bounty.

A Pentagon spokesman did not immediately return calls or e-mails seeking comment.

The judge issued the halt to Rahman's transfer pending a decision by the Supreme Court on detainee rights at the U.S. naval base in Cuba.

The high court has been asked to determine whether Guantanamo detainees can use civilian courts to challenge their indefinite imprisonment under an age-old right known as habeas corpus. The justices twice before have ruled that suspected terrorists could pursue such challenges in civilian courts, but each time, the Bush administration and Congress, then under Republican control, changed the law to try to limit the detainees' rights.

In her ruling, Kessler said "it is imperative" that her court "protect its jurisdiction until the Supreme Court issues a definitive ruling."