The names of hundreds of people detained since the 11 September attacks can be kept secret, a US federal appeals court has ruled.
The arrests follow the 11 September attacks on the World Trade Center
The decision overturns a federal court ruling that the names of those detained as part of anti-terrorism efforts since the 2001 attacks should be made public.
More than 20 civil liberties groups had argued that their names should be disclosed under the Freedom of Information Act.
But the appeals court backed the US Justice Department who said such information would play into the hands of terrorist groups.
Two of the three judges on the panel agreed that the government could keep secret the "dates and locations of arrests, detention and release of all detainees" as well as the names of lawyers representing suspects.
We are disappointed that for the first time in US history, a court has approved secret arrests
Center for National Security Studies
"While the name of any individual detainee may appear innocuous or trivial, it could be of great use to al-Qaeda in plotting future terrorist attacks or intimidating witnesses in the present investigation," said Judge David Sentelle.
The ruling is a blow to civil rights groups, led by the Center for National Security Studies, who have been denied information on foreigners detained since 11 September.
Kate Martin, director of the CNS, said: "We are disappointed that for the first time in US history, a court has approved secret arrests and we plan to pursue the case."
The panel's dissenting judge, David Tatel, said that while he acknowledged the government's reasons for seeking such a ruling, citizens' rights needed to be upheld.
"Just as the government has a compelling interest in ensuring citizens safety, so do citizens have a compelling interest in ensuring that their government does not, in discharging its duties, abuse one of its most awesome powers, the power to arrest and jail," he wrote.
In a report released earlier this month the Justice Department's inspector general found there had been "significant problems" in the way the US authorities had handled the round-up of suspects - mostly those of Pakistani origin - in the wake of the 11 September attacks.
More than 760 immigrants detained at the time were found guilty of violating US immigration law.
But the report found 54 of them had been detained for more than the 90 days allowed by anti-terrorist laws.
Another 130 had no lawyer, many of these because they were allowed only two telephone calls per month.