A US military judge at Guantanamo Bay said Thursday that federal investigators had carried out checks on the legal teams of at least two accused September 11 plotters, including alleged mastermind Khalid Sheikh Mohammed.
Judge James Pohl halted this week's preliminary hearings at Guantanamo after lawyers for the alleged terror plotters told the court that a member of the defense team had been visited and questioned by Federal Bureau of Investigation (FBI) agents.
David Nevin, representing the self-proclaimed 9/11 mastermind Khaled Sheikh Mohammed, said the FBI probe had had a "chilling effect" on the defense team.
After suspending proceedings in order to assess the extent of the claims, Pohl said Thursday it had been established that there had been "some type investigation by the FBI into Mr Mohammed's team."
Pohl ordered the appointment of an independent counsel to determine exactly what FBI investigators had obtained.
Pohl also said it had been established that a member of Ramzi Binalshibh's defense team had been a "co-operative source" for the FBI until at least as recently as April 6, creating the "appearance of a conflict of interest."
An independent counsel would also examine the details of those contacts, Pohl said.
The judge said there "may or not be a conflict" in the cases of the other three accused.
"I'm not sure there's a need for an independent counsel," he said, adding that defense lawyers for the men could submit requests in writing if they felt it necessary to conduct an independent investigation.
US government attorney Edward Ryan meanwhile also said a special prosecutor would be appointed to investigate the revelations.
The lawyers also said they wanted to question the FBI agents involved as well as a civil prosecutor in the case, Joanna Baltes, who was appointed chief of staff to the deputy director of the FBI.
The FBI had quizzed attorneys seeking to determine how one of Mohammed's personal documents had been smuggled out of the ultra-secure prison in Cuba.
Three inmates attended Thursday's hearing -- Mohammed, Binalshibh and Ali Abd al-Aziz Ali, Mohammed's nephew.
The three men face the death penalty if convicted of their roles in the 2001 attacks on New York and Washington which left nearly 3,000 people dead.
The next preliminary hearing is scheduled to be held in June at Guantanamo Bay. Thursday's hearing was screened live via video at Fort Meade military base in Maryland.