But the judges said that although Khadr and Hamdan had been classified "enemy combatants", they had not been tagged as "unlawful enemy combatants" as required by new rules drawn up by the US congress.
The Military Commissions Act that George Bush, the US president, signed last year, says specifically that only those classified as "unlawful" enemy combatants can face war trials, the judge in Khadr's case, Colonel Peter Brownback, noted during his arraignment.
|Prosecutors say Salim Ahmed Hamdan |
was bin Laden's driver [AFP]
The chief of military defence lawyers at Guantanamo Bay, Colonel Dwight Sullivan, said the decisions could spell the end of the war-crimes trial system.
Sullivan said the dismissals have "huge" impact because none of the detainees held at the isolated military base in southeast Cuba had been found to be "unlawful" enemy combatants.
"It is not just a technicality: it's the latest demonstration that this newest system just does not work," he told journalists. "It is a system of justice that does not comport with American values."
Sullivan said that to reclassify them as "unlawful", the whole review system would need a time-consuming overhaul.
But the Pentagon dismissed it as a technicality.
Navy Commander Jeffrey Gordon, a Pentagon spokesman, said: "It is our belief that the concept was implicit that all the Guantanamo detainees who were designated as "enemy combatants" … were in fact unlawful."
A prosecutor said he would appeal the dismissals, but the court designated to hear the appeal – known as the court of military commissions review – does not even exist yet, Sullivan noted.
The military tribunal process for detainees at Guantanamo has been controversial from the start.
Last year the US Supreme Court ruled in favour of a lawsuit brought by Hamdan.
In response to his petition, judges threw out an original tribunal system set up after the September 11, 2001 attacks in the US, calling it unconstitutional.
The US congress then came up with new guidelines for war crimes tribunals at Guantanamo - changes that helped lead to the dismissal of the cases against Khadr and Hamdan, who will remain at the Guantanamo prison.
Earlier this year, Guantanamo prosecutors struck a plea bargain deal with David Hicks, the so-called Australian Taliban who is now serving time in his own country – the only other Guantanamo detainee to go before a military tribunal so far.