The highest court in the U.S. blocked plans to bring back the death penalty on a federal level on Friday, days before a planned execution.
The U.S. Supreme Court denied an urgent application from the government to allow cases to resume after a 16-year hiatus, which effectively halted the executions of four men due to be put to death over the next few weeks, U.S. media including the New York Times reported.
Attorney General William Barr, seen as an arch-conservative, announced he was bringing back the death penalty in July, declaring that the federal government planned to execute five people convicted of murder, including a white supremacist.
President Donald Trump has been a long-time vocal advocate of the death penalty, going back to his days as an outspoken real-estate mogul.
As president, he has kept up a hard-line approach.
U.S. states individually decide whether to use capital punishment in their criminal justice systems.
The federal system is separate to those of the 50 states and other jurisdictions.
Some 20 states have banned the death penalty, while others have not carried out executions in decades.
The last time the federal government executed someone was in 2003, one of only a small handful of such cases since the death penalty was reinstated at the federal level in 1988.
Part of the legal challenge to the use of the death penalty at the federal level relates to appeals over the protocol of execution, which is lethal injection.