After U.S. officials unveiled the evidence to reporters in Baghdad two weeks ago, however, Secretary of Defense Robert M. Gates and other Pentagon officials scrambled to retreat from the incendiary claim that the "highest levels" of the Tehran government were directly involved.
"I don't know if it goes to the highest levels of the government," Army Lt. Gen. Raymond T. Odierno, the officer in charge of daily operations in Iraq, told Pentagon reporters Thursday. "What we do know is that the Quds Force has had involvement with some extremist groups in Iraq."
Washington has sought to pressure Tehran into halting the supply of "explosively formed projectiles" that are able to penetrate heavily armored vehicles. The projectiles represent only a small percentage of roadside bomb attacks in Iraq, but they are far more lethal than ordinary explosives.
Administration officials also cite a growing effort by the militant group Hezbollah, an Iranian protege and ally based in Lebanon, to aid anti-American Shiite forces in Iraq.
U.S. military officials contend that Hezbollah has provided training in Lebanon to hundreds of members of the Al Mahdi militia, which is controlled by radical anti-American cleric Muqtada Sadr. A smaller number of Hezbollah forces reportedly have entered Iraq through Syria to provide such training.
The administration has ordered a second aircraft carrier group into the Persian Gulf, a reminder that President Bush could order an airstrike on Iran's nuclear sites even while U.S. forces are tied down in Iraq. But White House officials have denied that an attack is imminent.
Given the lack of clear evidence, Iran's strategic goals in Iraq are a matter of debate, and concern has spread about its growing influence there. Although Iran is mostly Persian and Iraq is mostly Arab, both have majority Shiite populations that have kept close religious, economic and cultural ties for centuries. Iran's rulers view the U.S. as meddling in their backyard, or at least in their sphere of influence.
Some outside experts think the Islamic Republic seeks to keep the United States tied down indefinitely in Iraq and will actively resist a settlement there for fear that Washington will next turn its guns on Iran.
Ali Ansari, an expert on Iran at St. Andrews University in Scotland and author of "Confronting Iran," counters that Iran and America share some interests.
