For all the aggressive rhetoric, however, the Bush administration has provided scant evidence to support these claims. Nor have reporters traveling with U.S. troops seen extensive signs of Iranian involvement. During a recent sweep through a stronghold of Sunni insurgents here, a single Iranian machine gun turned up among dozens of arms caches U.S. troops uncovered. British officials have similarly accused Iran of meddling in Iraqi affairs, but say they have not found Iranian-made weapons in areas they patrol.
The lack of publicly disclosed evidence has led to questions about whether the administration is overstating its case. Some suggest Bush and his aides are pointing to Iran to deflect blame for U.S. setbacks in Iraq. Others suggest they are laying the foundation for a military strike against Iran.
Before invading Iraq, the administration warned repeatedly that Saddam Hussein was developing nuclear, chemical and biological weapons. Those statements proved wrong. The administration's charges about Iran sound uncomfortably familiar to some. "To be quite honest, I'm a little concerned that it's Iraq again," Sen. John D. Rockefeller IV, head of the Senate Intelligence Committee, said last week, referring to the administration's comments on Iran.....
"We are still making arguments from authority without detail and explanation. We're making them in an America and in a world where we really don't have anything like the credibility we've had in the past."
Few doubt that Iran is seeking to extend its influence in Iraq. But the groups in Iraq that have received the most Iranian support are not those that have led attacks against U.S. forces. Instead, they are nominal U.S. allies.
The Supreme Council for Islamic Revolution in Iraq, one of the two largest parties in parliament, is believed to be the biggest beneficiary of Iranian help. The Shiite group was based in Iran during Hussein's reign, and Iran's Revolutionary Guard trained and equipped its Badr Brigade militia.
But the Supreme Council also has strong U.S. connections. Bush played host to the head of the party, Abdelaziz Hakim, at the White House in December, and administration officials have frequently cited Adel Abdul Mehdi, another party leader, as a person they would like to see as Iraq's prime minister.
The Islamic Dawa Party of Iraq's current prime minister, Nouri Maliki, also has strong ties to Iran.
Some U.S. officials have also suggested that Iran, a Shiite theocracy, has provided aid to the Sunni insurgents, who have led most of the attacks against U.S. forces. Private analysts and other U.S. officials doubt that.