The five plaintiffs were returning by car from a religious conference in Toronto in December.

The suit accuses the government of violating the group's constitutional freedom of religion and protection against unlawful searches.

US customs has defended its procedures at border check-points.

The plaintiffs want no monetary damages but an end to such detentions.

'Unbelievable'

The suit brought by the New York Civil Liberties Union and other groups names the current head of homeland security, Michael Chertoff, as one of four defendants.

The five were part of a group of at least three dozen Muslim men and women who were stopped after returning from the annual "Reviving the Islamic Spirit" conference in Toronto in December 2004.

The plaintiffs said they were forced to hand over credit cards and other belongings and were searched, questioned, photographed and fingerprinted without explanation.

One of the plaintiffs, Sawsaan Tabbaa, said she had been told she was being pulled aside because of a random selection but then she saw other Muslims who had attended the conference.

"I am proud of being American but I couldn't believe my eyes something like this could happen," she said.

Those detained have never been charged with any crime.

Agency defends practices

US Customs and Border Protection spokeswoman Kristie Clemens declined to comment on the specific case as it was in litigation but she said the service's priority was to "prevent terrorists and their weapons from entering" the US.

The identity of people wishing to cross the border must be verified and fingerprinting is one way to do that, she added.

According to the agency, terrorist organisations have been using conferences like the one in Toronto to promote their cause and raise money.

The plaintiffs want an injunction that would bar the government from such detentions in the future and they also want the fingerprints and photographs taken that night to be expunged from government records.