A judge has delayed an upcoming hearing for five men accused of plotting the September 11 attacks due to suspicions that confidential defense emails were monitored, a lawyer said Wednesday.

The next preliminary hearing had been set to take place on April 22 at the US military base at Guantanamo. It was now scheduled for June 17-21, according to a Pentagon spokesman.

Lawyers for four of the accused had filed an emergency motion with presiding Judge Colonel James Pohl, seeking a delay in proceedings after revelations that defense emails and computer files had been compromised.