US officials are preparing to detail evidence supporting the Bush administration's claims that Iran is providing lethal help to Iraqi fighters, in a briefing scheduled Sunday in Baghdad. The Iran dossier, some 200 pages thick in its classified form, was revised heavily after officials decided it was not ready for release as planned last month. What is made public probably would be short, and shorter on details than the administration recently had suggested. No one who has seen the files has suggested the evidence is thin. But the Bush administration is haunted by the history of intelligence blunders about Saddam Hussein's supposed weapons of mass destruction that led up to the 2003 Iraq invasion. Officials from several intelligence agencies scrutinized the presentation to make sure it was clear and that "we don't in any way jeopardize our sources and methods in making the presentation," State Department spokesman Sean McCormack said Friday. National security adviser Stephen Hadley recently said some Iran material was overstated. Privately, officials say they want to avoid the kind of gaffe akin to former Secretary of State Colin Powell's case for war before the United Nations in 2003. "My colleagues, every statement I make today is backed up by sources, solid sources. These are not assertions," Powell said as he laid out unproven claims of Iraq's weapons of mass destruction. "What we're giving you are facts and conclusions based on solid intelligence." It later turned out that Iraq did not have such weapons. The evidence on Iran is intended to give backbone to the administration's claim that an emboldened Iran is playing a dangerous game across the Middle East: meddling in conflicts and seeding terrorism beyond its borders while rushing to acquire nuclear know-how that could produce a bomb. Government officials familiar with the dossier's documents and slides, who spoke on condition of anonymity because the materials still were classified, said they make a compelling case about Iranian actions in Iraq. Among the evidence the administration planned to present are weapons that were seized over time in US-led raids on caches around Iraq, said one military official. Other evidence includes documents captured when US-led forces raided an Iranian office Jan. 11 in Irbil, a city in Kurdish-controlled northern Iraq about 220 miles (355 kilometers) north of Baghdad, this official said. In that raid, the US captured five Iranians. They included the operations chief and other members of Iran's elite Quds Force, which is accused of arming and training Iraqi militants. Tehran said it was a government liaison office and called for the release of the five, along with compensation for damages. The dossier also details Iran's role in providing Iraqi fighters with the "explosively formed penetrator" devices that can pierce the armor of Abrams tanks with nearly molten-hot charges. One intelligence official said the US is "fairly comfortable" that it knows with some precision the origin of those Iranian-made explosives. While traveling in Europe on Friday, Defense Secretary Robert Gates said that serial numbers and markings on explosives used in Iraq provide "pretty good" evidence that Iran is providing either weapons or technology for militants there. Gates did not how the US knows that, and officials in Washington declined comment. A senior US government official said Saturday that members of Congress were shown proof in December. "I'm convinced from what I've seen that the Iranians are supplying and are giving assistance to the people in Iraq who are killing American soldiers," said independent Senator Joe Lieberman. The evidence in the dossier also includes what is known about Iranian efforts to train Iraqis in making bombs, using firearms and other military skills. But officials described internal disagreement about how closely Iranians can be linked to the training: Is there an Iranian in a classroom or some other setting showing Iraqis how to place and detonate roadside bombs? That, the official said, is less clear. Analysts at the Defense Intelligence Agency, the Office of the National Intelligence Director and elsewhere have been double- and triple-checking the information to ensure it is well supported. Officials said that is particularly the case when the material comes from sources with agendas. For instance, groups such as the Mujahedeen Khalq, which advocates for the overthrow of Iran's rulers, have provided some useful information to the United States in the past, but officials said material from them and other similar sources must be handled carefully. The vigorous fact-checking brings up a recurring problem: the precise nature of Iran's actions is often murky, but the intelligence must be solid. After mistakes on Iraq's weapons of mass destruction, US officials recognize there is skepticism about US intelligence claims.