WASHINGTON (AFP) - Unfounded intelligence claims that paved the way for war in Iraq blew back like a ghost last week to haunt US charges that Iran is arming Iraqi extremists.

President George W. Bush and his top aides had to admit by week's end that they did not know whether Iran's leaders knew that the Iranian Revolutionary Guard was supplying Shiite militias with sophisticated bombs and training.

And "for the umpteenth time," as US Defense Secretary Robert Gates put it, they denied that the United States was trying to prepare the ground for military action in Iraq.

But the flap exposed how deep public suspicion of US intelligence claims runs nearly four years after the United States went to war with Iraq on the strength of erroneous intelligence that it had weapons of mass destruction.

"I think this controversy is traceable to one big problem," said Loren Thompson, director of the Lexington Institute, a private Washington research group.

"The US intelligence community does not have an adequate network of agents in Iraq or Iran. Because of that, everything is guesswork," he said.

"We accumulate a lot of disconnected details, and we try to form a pattern out of those details, but we never have that final definitive piece of intelligence that proves the connection," he said.

Officials said US intelligence spent weeks vetting the accuracy of the information before it was briefed to reporters in Baghdad on Sunday.

Reporters were shown examples of weapons, including an armor-piercing bomb known as an "explosively formed penetrator" or EFP, that the US military said are being supplied to extremists by Iran.

Briefing slides contained photographs of EFP caches, passive infrared triggers, blocks of TNT and a blasting cap, mortar rounds, a man-portable surface-to-air missile, and rocket-propelled grenades -- all allegedly made in Iran.

It said Iranians arrested in a recent raid in the northern Iraqi city of Irbil were members of the Iranian Republican Guards, and that its paramilitary Qods Force was providing advice, training and weapons to extremist groups.

The briefing slides cited markings on some of the weapons that indicated they were Iranian-made.

Gates, a former CIA director, told reporters that he had insisted on factual statements with no adjectives or adverbs, only declarative sentences that "make it exactly clear what we know and what we don't know."

The reason, he indicated, was because he expected there would be doubts about the intelligence.

"I mean, we're sensitive to that skepticism," he said Thursday.

"And it's one of the reasons why we were so concerned that the briefing on these materiels be factual and be able to be substantiated by evidence, so it wasn't hypothesis, it wasn't assumption, it wasn't assessment."

But an unidentified briefer apparently went further and was reported to have said the support was sanctioned by the "highest levels" of the Iranian regime, sparking the intense round of speculation about US intentions.

"I think there's no question that the skepticism has less to do about competing explanations than just generalized doubt about the administration's judgment," said Thompson.

"You really can prove that the munitions in question came from Iran. But the question is what interpretation to make of that. And on that score the public really doesn't much trust the White House's interpretation of events," he said.

The allegations themselves were not new, which suggested to some analysts that the briefing was timed to step up pressure on Iran at a time when a diplomatic confrontation over its nuclear program is reaching a critical stage.

Bush had already ordered a second aircraft carrier to the Gulf and stepped up raids in Iraq on networks supplying Iranian arms to Iraqi militias.

"I think it has to do with a whole new policy toward Iran which is more confrontational," said Vali Nasr, an expert at the Council on Foreign Relations, in an interview carried on its website.

"Putting Iran in the spotlight in Iraq is a part of a policy of escalating pressure on Tehran, as well as also potentially preparing the American population for more drastic action against Iran by trying to single out Iran as the problem in Iraq, whether or not that's actually true," he said.

John Pike, director of GlobalSecurity.Org, said the briefing aroused controversy because "it really looks like Mr. Bush is getting ready to bomb Iran."

But there were other reasons as well. The evidence was unconvincing and "their credibility was shot after the intelligence failure around Iraq," he said.

Commentary: