BAGHDAD, Iraq — Three U.S. defense officials Sunday accused the Iranian government of providing Shiite Muslim militias in Iraq with parts for sophisticated armor-piercing improvised bombs that they said have killed 170 coalition troops.

"We need Iran to stop doing what they're doing," one of the officials said. "It's a force-protection issue."

The officials Sunday accused the Iranian Revolutionary Guard's Quds force of providing the devices, but one of them acknowledged that there's no "smoking gun" against Iran.

The three officials refused to let their names be used, and although the briefing was filmed for government use, reporters weren't allowed to have recorders, cell phones or cameras. The officials said they were releasing the information to get the Iraqi government to pressure the Iranians to stop.

The new allegations come amid escalating tensions over Iran's alleged nuclear weapons program and new evidence that many of the Bush administration's claims about Saddam Hussein's weapons programs and links to al-Qaida were erroneous.

The evidence of Iranian meddling in Iraq, however, is far more compelling than much of the administration's pre-war intelligence about Iraq. Iran's clerical regime has long armed, advised and trained Iraqi Shiite militias, and it's supplied the militant Lebanese Shiite group Hezbollah with sophisticated bombs similar to those used against U.S., coalition and Iraqi troops in Iraq.

"Iran does not deny outside interference," said an Iraqi government official with knowledge of meetings between the Iranian and Iraqi governments, who declined to speak on the record because the issue is politically sensitive. "Iran actually says, 'Yes, we are interfering.' They justify this by saying, 'The Americans and the British are threatening our security, and we have to take measures to react."'

Sunday's allegations were based on some Iranian weapons, including the armor-piercing devices, 81 mm mortars and rocket-propelled grenades, which were seized in Shiite areas of Iraq, the U.S. officials said. The evidence of Iranian activity also included two identification cards that were seized in a raid on an Iranian liaison office in the northern Iraqi city of Irbil; the evidence was also based on interrogations of Iranian and Iraqi detainees.

Since June 2004, the armor-piercing bombs have killed 170 coalition troops, about 5 percent of the coalition forces killed in Iraq. The officials Sunday said that such attacks have increased during the past six months, but one senior defense official refused to provide a number to support the claim.

Two of the Shiite militias that the U.S. officials said are being armed and trained by Iran, the Mahdi Army of anti-American cleric Muqtada al-Sadr and the Badr Organization of the Supreme Council for the Islamic Revolution in Iraq, are allied with the U.S.-backed government of Iraqi Prime Minister Nouri al-Maliki.

Iraqi Shiite politicians have begun to claim that renegade elements of the Mahdi Army are mounting sectarian attacks in Baghdad, but on Sunday a senior U.S. defense analyst said it wasn't clear whether these were covert Mahdi Army attacks or the work of "rogue" elements of the group.

The analyst said although it has close ties to Iran, the Badr Organization itself "has never been a part of anti-coalition attacks," but that some of the Iranian support is going to a group lead by Abu Mustafa Shaabani that split from the main group in 2003.