A German citizen who said he was kidnapped by the Central Intelligence Agency and tortured in a prison in Afghanistan lost his last chance to seek redress in court today when the Supreme Court declined to consider his case.

The justices’ refusal to take the case of Khaled el-Masri let stand a March 2 ruling by the United States Court of Appeals for the Fourth Circuit, in Richmond, Va. That court upheld a 2006 decision by a federal district judge, who dismissed Mr. Masri’s lawsuit on the grounds that trying the case could expose state secrets.

The Supreme Court’s refusal, without comment, to take the case was not surprising, given that a three-judge panel for the Fourth Circuit was unanimous. Nevertheless, today’s announcement prompted immediate expressions of dismay, and it could exacerbate tensions between the United States and Germany.

The Fourth Circuit acknowledged the seriousness of the issues when it dismissed Mr. Masri’s suit. “We recognize the gravity of our conclusions that el-Masri must be denied a judicial forum for his complaint,” Judge Robert B. King wrote in March. “The inquiry is a difficult one, for it pits the judiciary’s search for truth against the executive’s duty to maintain the nation’s security.”

After 23 days, he said, he was turned over to C.I.A. operatives, who flew him to a secret C.I.A. prison in Kabul. There, Mr. Masri said, he was kept in a small, filthy cell and was shackled, drugged and beaten while being interrogated about his supposed ties to terrorist organizations. At the end of May 2004, Mr. Masri said, he was released in a remote part of Albania without ever having been charged with a crime.