A US federal judge on Friday revoked an order allowing the release of the Orlando nightclub killer's widow pending trial, saying she posed a flight risk and danger to the public.
Florida US District Judge Paul Byron reversed an earlier decision by a federal magistrate in California to release Noor Salman on $500,000 bail.
"Upon consideration, this court finds that no condition or combination of conditions of pretrial release will reasonably assure the safety of the community or reasonably assure the defendant's appearance during the required court proceedings," the judge wrote.
Omar Mateen's mass shooting at Pulse, a gay nightclub in Florida, last June killed 49 people and left at least 68 others wounded.
Mateen, who pledged allegiance to the Islamic State (IS) jihadist network in a 911 call during the attack, was killed in a shootout with police. He was 29.
Salman, 30, was arrested in January in northern California, where she has family, for aiding and abetting her husband -- a charge that carries a sentence of up to life in prison.
She has also been charged with lying to investigators.
Magistrate Donna Ryu's decision last week to release Salman on bond was put on hold pending an appeal by prosecutors.
Byron said while Ryu found the evidence in the case to be "debatable" he disagreed with that assessment.
He said although Salman may not be directly linked to IS, she was well aware of her husband's extremist views and that he was planning an attack, as shown in her alleged admissions to the Federal Bureau of Investigation.
Her attorneys argue, however, that any admissions Salman may have made came at the end of a 16-hour interview.
Byron in his ruling also said he was not persuaded by family and friends who have spoken favourably of Salman -- who had a four-year-old son with Mateen -- in sworn statements.
"The existence of the defendant's past involvement in a terrorist attack, even recognising she did not pull the trigger, poses too great of a danger to the community to warrant pre-trial release," Byron wrote.
He added that although both Salman's uncle and her mother had agreed to put their houses in California up as collateral if she were released, he feared she might flee to the West Bank in Palestine, where the family owns property.
Salman's attorney Charles Swift said in a statement that his client maintains her innocence.
"She persists in her claim of innocence and we are currently exploring all available legal remedies on her behalf," he said in a statement. "Until all the facts come out in trial, we urge the community to withhold judgment."