A court on Wednesday barred the British government from providing U.S. prosecutors with evidence against two Islamic State militants suspected in the beheadings of Western hostages, citing the prospect the men could face the death penalty if tried and convicted in America.

The ruling by the British Supreme Court blocks an earlier decision by the country’s authorities to cooperate with the U.S. by sharing information about El Shafee Elsheikh and Alexanda Kotey.

The British men, captured two years ago by a Kurdish-led, U.S.-backed militia, are accused of participation in a brutal Islamic State group known for beheadings and barbaric treatment of American aid workers, journalists and other hostages in Syria.

The court decision is a setback for the U.S. Justice Department, where officials for years have been investigating the killings. U.S. officials have not announced any charges against the men, but have spoken publicly about their desire to see members of the cell, known as “The Beatles” for their British accents, face justice. The men were transferred to U.S. custody last October as Turkey invaded Syria to attack Kurds who have battling the Islamic State alongside American forces.

“We are disappointed with the UK Supreme Court’s decision and are considering the appropriate next steps,” said Justice Department spokesman Marc Raimondi. “As our investigation of these individuals continues, we will work with our UK counterparts on a path forward, consistent with our shared commitment to ensuring that those who commit acts of terror are held accountable for their crimes.”

It was not clear what those next steps would be, or whether the decision might prompt the Justice Department to remove the possibility of the death penalty from any eventual prosecution. Attorney General William Barr said in a private meeting last year with victims’ relatives that he wanted to see the militants brought to justice.