A U.S. military judge called off a pretrial hearing for five Guantánamo Bay detainees accused of playing a role in the Sept. 11 attacks against the American homeland, said a Pentagon spokesman.

The cancellation was described by Reuters as “another setback for the government in its efforts to try the five men being held at Guantanamo.”

A Pentagon spokesman revealed that the military judge trying the case cancelled the hearing, which was scheduled for Aug. 24 to Sept. 4.

“The judge cited issues that remain unresolved with regard to a claimed defense counsel conflict of interest,” Commander Gary Ross reportedly said.

ABC News first reported that the hearing had been cancelled.

“Defense attorneys for Khalid Sheikh Mohammed and four alleged co-conspirators raised concerns in 2014 that they were being spied on by the Federal Bureau of Investigation,” notes Reuters. “They said that created a conflict of interest between them and their clients. Judge James Pohl, an Army colonel, ruled in July that no conflict of interest arose for defense attorneys.”

“The allegations have further delayed a complex, slow-moving case, one of a number being held at the facility at the Guantanamo Naval base in Cuba, where suspects in the post-Sept. 11 ‘war against terrorism’ are detained,” it adds.

If found guilty, the five defendants could be sentenced to death for their key roles in the Sept. 11 attacks.

The recent cancellation provides ammo to critics of the military trials in Guantánamo who argue that the inability of the government to try the defendants more than 10 years after their capture is a clear sign of the undertaking’s failure.

President Obama has promised to shut down the U.S. detention facility in Guantánamo Bay but has met resistance in Congress.

News of the hearing’s cancellation came after the Associated Press (AP) reported that the Pentagon is looking at prisons inside the United States as an alternative to Guantánamo.

“The Defense Department is taking another look at the military prison in Kansas and the Navy Brig in South Carolina as it evaluates potential U.S. facilities to house detainees from the prison at Guantanamo Bay, Cuba, part of the Obama administration’s controversial push to close the detention center,” said the AP report.