WASHINGTON: Families of the victims killed on September 11, 2001 have branded a decision to try the suspected plotters in a civilian New York court as "a terrible mistake."

"To allow a terrorist and a war criminal the opportunity of having US constitutional protections is a wrong thing to do and it's never been done before," Ed Kowalski of the 9/11 Families for a Secure America Foundation said yesterday.

The alleged mastermind, Khalid Sheikh Mohammed, and four others will be tried in the Southern District, near Ground Zero, once the site of the World Trade Centre.

Republican Senator Jon Kyl said bringing Khalid to New York was "an unnecessary risk" that could result in the disclosure of classified information.

Five others, including a major suspect in the bombing of the USS Cole warship, will be tried before a military commission.

The decision comes just before a Monday deadline for the government to decide how to proceed against the detainees facing commissions.