The US Supreme Court has denied an appeal by the state of Alabama to execute death row prisoner Jeffery Lee using nitrogen gas.
Two lower courts had earlier blocked the use of nitrogen gas in executions, finding the method likely violates the US Constitution's ban on cruel and unusual punishment. Alabama then appealed that ruling.
The brief, unsigned order on the Supreme Court's emergency docket did not provide an explanation, but Justices Clarence Thomas, Samuel Alito and Neil Gorsuch dissented, indicating that they would have granted the state's request.
Alabama's top prosecutor said the halted execution is "a miscarriage of justice" for the state and the families of the victims.
Alabama has executed seven people using nitrogen gas since introducing the method in January 2024, one of the few states to do so.
Death by nitrogen hypoxia - when a death penalty inmate is forced to breathe pure nitrogen through a gas mask until they suffocate - was permanently banned by a federal judge this week after experts and witnesses provided testimony during an April bench trial.
The lower court, which reversed a previous decision by an appeals court, found inmates executed by the relatively new form of capital punishment likely experience "severe air hunger and corresponding emotional distress, anxiety, physiological stress, and physical discomfort" before asphyxiation occurs, according to the BBC's US media partner, CBS News.
Alabama filed an emergency order on Thursday, just hours before the scheduled execution Lee, 49, who was to be put to death at 18:00 local time.
Lee was convicted of murdering two people in a 1998 pawnshop robbery and has been on Alabama's death row for more than two decades. A jury recommended that he be sentenced to life in prison, but a judge overturned the jury's decision and sentenced him to death under a since-abolished judicial override procedure.
The state can still seek to put Lee to death using another execution method.
Alabama Attorney Genera Steve Marshall said in a statement that the halted execution is unfair to the families of Lee's victims, who "were prepared to witness the final act of justice be served".
He added: "The State is prepared to do whatever is necessary to see Mr Lee's lawful sentence carried out."
BBC