The US Supreme Court has agreed to hear an appeal by Guantanamo Bay detainees that they be allowed to challenge their confinement in federal courts.
The US is facing growing calls to close down Guantanamo Bay
The move reverses the court's decision in April, when it refused to rule on whether the men had a right to take their cases to federal courts.
This latest move is a blow to the US government, which wants the cases to be dealt with by military tribunals alone.
Hundreds of men have been held without charge for years at Guantanamo Bay.
The treatment of the men has been heavily criticised by international human rights bodies and foreign governments, including some allies of the US.
Allegations of abuse have dogged the camp, many of whose inmates were captured in 2001 and 2002, in the early days of the "war on terror".
The administration last year pushed a law through Congress that prohibited Guantanamo Bay detainees from challenging their confinement in federal courts.
Under the law, detainees' cases could only be heard in military commissions - not in civilian courts.
In February this year, an appeals court hearing in the District of Columbia upheld this law.
In April, the US Supreme Court rejected the detainees' request to hear an appeal on the February ruling.
The detainees' lawyers said dismissing the cases would be a "profound deprivation" of the prisoners' rights and urged the Supreme Court to reconsider its decision - a request that has now been granted.
The court is expected to hear the detainees' cases when it begins a new term in October.
US military lawyers are among those who have criticised the military commissions, describing them as inadequate for trying the detainees.
'Risk to sanity'
A Bush administration spokesman defended the government's stance on Guantanamo Bay.
"We did not think that court review at this time was necessary, but we are confident in our legal position," Gordon Johndroe of the National Security Council said.
A US lawyer representing some of the men imprisoned at Guantanamo Bay welcomed the Supreme Court decision.
Sabin Willet told the BBC News website he was "highly optimistic" the court would rule in his clients' favour after its "very unusual" reversal.
"Now that they are in their sixth year of captivity, the only question is whether these men will still be sane by the time a court actually hears their case," he said.