While it found no operational ties between al Qaeda and Iraq, the commission investigating the Sept. 11, 2001, attacks has concluded that Osama bin Laden's terrorist network had long-running contacts with Iraq's neighbor and historic foe, Iran.

Al Qaeda, the commission determined, may even have played a "yet unknown role" in aiding Hezbollah militants in the 1996 bombing of the Khobar Towers complex in Saudi Arabia, an attack the United States has long blamed solely on Hezbollah and its Iranian sponsors.

The notion that bin Laden may have had a hand in the Khobar bombing would mark a rare operational alliance between Sunni and Shiite Muslim groups that have historically been at odds. That possibility, largely overlooked in the furor of new revelations released by the commission last week, comes amid worsening relations between the United States and Iran, which announced on Thursday that it would resume building equipment necessary for a nuclear weapons program.