WASHINGTON (Reuters) - The U.S. military has canceled a pretrial hearing for suspects in the Sept. 11, 2001 attacks, a military spokesman said on Sunday, in another setback for the government in its efforts to try the five men being held at Guantanamo.

A defense department spokesman said the hearing, originally scheduled for Aug. 24 to Sept. 4, was canceled by the military judge.

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

News of the cancellation was first reported by ABC News.

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. 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.

Critics of the military trials in Guantanamo have said the inability of the government to try the defendants more than a decade after their capture is one of the clearest signs of the failure of the process.

The five defendants, who were captured in 2002 and 2003, could be put to death if convicted of key roles in the Sept. 11 attacks, which killed about 3,000 people.

(Reporting by Yeganeh Torbati and David Rohde, editing by Larry King)