SAN FRANCISCO -- A Boeing Co subsidiary prevailed on Wednesday against a lawsuit alleging it had helped the CIA illegally transport prisoners to secret facilities overseas, a federal appeals court has ruled.

The 9th Circuit U.S. Court of Appeals in San Francisco dismissed the lawsuit against Jeppesen Dataplan Inc, finding that rules protecting state secrets made it impossible for the litigation to proceed. The U.S. Department of Justice intervened in the case on behalf of Jeppesen.

A group of plaintiffs represented by the American Civil Liberties Union claimed that they were tortured in the foreign prisons. An earlier three-judge panel of the 9th Circuit had allowed the lawsuit, but the fuller court voted 6-5 on Wednesday to dismiss the case.

"We ... acknowledge that this case presents a painful conflict between human rights and national security," 9th Circuit Judge Raymond Fisher wrote.

A Jeppesen spokesman referred questions to the Justice Department, which declined to comment. On cases involving state secrets the Obama administration has often taken legal positions consistent with those of its Republican predecessor.

ACLU staff attorney Ben Wizner said the organization "absolutely" intends to seek U.S. Supreme Court review of the case.

"If the U.S. does not provide for judicial remedies, it is all the more likely that foreign judges and prosecutors will reopen and reinvigorate their investigations into the crimes alleged in this case," he said.

The case in the 9th Circuit is Mohamed v. Jeppesen Dataplan, 08-15693.