The Bush administration's plans to bring detainees at Guantánamo Bay to trial were thrown into chaos yesterday when military judges threw out all charges against a detainee held there since he was 15 and dismissed charges against another detainee who chauffeured Osama bin Laden.

In back-to-back arraignments for the Canadian Omar Khadr and Salim Ahmed Hamdan, a Yemeni national, the US military's cases against the alleged al-Qaida figures were dismissed because, the judges said, the government had failed to establish jurisdiction.

Article continues Yesterday's decision by Colonel Peter Brownback to dismiss all charges against Mr Khadr on technical grounds has broad implications for the Bush administration's system of military tribunals because the technicality appears to apply to all 385 prisoners held at Guantánamo.

The dismissal of the case also undermines the administration's efforts to show that the military tribunals are based on sound legal practice and can provide detainees with a fair hearing, detainee lawyers said.

In his decision yesterday, Col Brownback said the Pentagon had merely designated Mr Khadr, a Canadian citizen facing charges of murder and terrorism, as an "enemy combatant", not an "unlawful enemy combatant", the term used by Congress last year in authorising the tribunals.