The unanimous decision came in the cases of Shawqi Omar, taken into custody in Iraq for allegedly assisting a terrorist network, and Mohammad Munaf, whose death sentence by an Iraqi court was recently overturned. Munaf has been accused in Iraq of setting up the 2005 kidnapping of three Romanian journalists.

Held by the U.S. military at Camp Cropper near Baghdad International Airport, both men are Sunni Muslims who say they will be tortured if turned over to the Iraqi government.

Chief Justice John Roberts wrote that U.S. courts are not allowed to intervene in an ongoing foreign criminal proceeding and "pass judgment on its legitimacy."

The justices ruled that basic protections do extend to American citizens held overseas by U.S. military operating as part of a multinational force. At the same time, however, the court said those protections provide Omar and Munaf with no legal relief.

The Bush administration argued that U.S. courts lack authority to review the claims of Munaf and Omar because they are held abroad by a multinational force, of which the United States is only a part.

Nations including Iraq have criminal jurisdiction over those within their borders, said the Justice Department solicitor general's office.

Arrested in 2004 by U.S. soldiers at his home in Baghdad, Omar was to have been transferred to Iraqi courts for trial, but a U.S. district court blocked the move.

In a case that is continuing, an Iraqi court recently reversed Munaf's death sentence.