A federal judge, saying the case involved a state secret, dismissed a lawsuit on Wednesday against a unit of Boeing that charged the firm helped fly terrorism suspects abroad to secret prisons.

The American Civil Liberties Union filed a complaint in May accusing Jeppesen Dataplan of providing flight and logistical support to the U.S. government with at least 15 aircraft on 70 "extraordinary-rendition" flights.

"In sum, at the core of plaintiffs' case against Defendant Jeppesen are 'allegations' of covert U.S. military or CIA operations in foreign countries against foreign nationals - clearly a subject matter which is a state secret," Judge James Ware wrote in a ruling issued on Wednesday evening.

The court "grants the United States' motion to dismiss on the ground that the very subject matter of the case is a state secret."

The complaint to the U.S. District Court for the Northern District of California alleged Jeppesen "falsified flight plans to European air traffic control authorities to avoid public scrutiny of CIA flights."

The ACLU filed the suit on behalf of five men who say the CIA had them flown to foreign prisons for interrogations and torture. The plaintiffs are an Ethiopian living in Britain; an Italian who was working in Pakistan; an Egyptian citizen living in Sweden; a Yemeni; and an Iraqi who is a British resident.

The government argued the case should be dismissed because they could not confirm details of the operations.

Those details "include whether any private entities or other countries assisted the CIA in conducting the program; the dates and locations of any detentions and interrogations; the methods of interrogation employed in the program; and the names of any individuals detained and interrogated by the CIA (other than fifteen individuals whose identities have been divulged so that they can be brought to trial)," the U.S. government said in its filing last year.

The judge mentioned he had reviewed a classified declaration from Michael Hayden, director of the CIA, in its assessment of the case.

"The Court's review of General Hayden's public and classified declarations confirm that proceeding with this case would jeopardize national security and foreign relations and that no protective procedure can salvage this case," Ware wrote.