The 14 detainees - described by the US as "high-value" suspects - were transferred to the US navy base in Cuba in September after years held in secret CIA prisons.
Peppler said some are expected to boycott the proceedings and their hearings will be held in absentia.
The Pentagon closed the proceedings to the media for the first time since the panels started in 2005. The only account of the hearings will come from the US military. Lawyers for the suspects have also been shut out.
The suspects include Khalid Sheikh Mohammed, the alleged mastermind of the attacks on September 11, 2001, as well as Ramzi bin al-Shibh, suspected of being a conspirator, Abu Zubaydah, suspected of being an Osama bin Laden aide, and Hambali, identified by one name, who is alleged to have organised bombings in Bali in 2002.
Legal experts have criticised the US decision to bar independent observers from the hearings and The Associated Press filed a letter of protest, arguing that it would be "an unconstitutional mistake to close the proceedings in their entirety".
Human rights groups and some former military lawyers say the secretive approach further damages US credibility over its treatment and prosecution of "terror" suspects.
Amnesty International said: "The USA's treatment of the 14 over the years has transformed them from individuals with allegedly high intelligence value to detainees with information about possible government crimes, including enforced disappearance."
The Center for Constitutional Rights (CCR), which is organising the defence of hundreds of Guantanamo detainees, said barring detainees from access to lawyers or the media aims to "prevent torture and abuse from becoming public, and to protect any foreign governments who may have assisted or been complicit".
Scott Silliman, who was a US air force lawyer for 25 years, said: "The whole world is watching. If congress enacts what it claims to be a fair system for prosecuting these people, why is there a need to shield it from the press?''
Bryan Whitman, a Pentagon spokesman, said the hearings were closed to prevent classified information from leaking.
Whitman said the Pentagon will release a redacted transcript of the proceedings as soon as possible and post it on a Pentagon website along with an unclassified summary of the evidence against the detainees.
Officials would not say which of the 14 would go first, how many have refused to take part in the proceedings and declined to offer a schedule for the hearings.
Initially, the Pentagon planned to withhold the names of the detainees from the transcripts, but later reconsidered.
The status review panels are not attempting to rule on an inmate's guilt or innocence. But a decision to keep the suspects under detention is expected to pave the way for formal trials on terrorism charges before special military tribunals created by the US congress under a controversial law.
The other 370 Guantanamo detainees have all passed through similar status review boards, in which a shackled prisoner, without a legal advocate, is presented with a brief summary of the allegations he faces.
|Human rights groups frequently|
protest against the jail [AFP]
Only rarely in the status review procedures have detainees been able to cite witnesses or offer documents in their favour.
The Pentagon says such a procedure permits the US to balance the threat posed by the suspects and the desire not to hold them in custody longer than necessary.
George Bush, the US president, has come under severe international criticism for holding detainees without charges at the naval base in Cuba amid allegations of abuse and torture.
Human rights groups and European governments have condemned the detention camp as flouting fundamental civil liberties and demanded the prison be closed.
Some legislators in the Democratic-controlled US congress have also called for closing the camp and possibly transferring some detainees to prisons on the US mainland.