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WASHINGTON (CNN) -- President Bush said Wednesday that "a part of the Iranian government" is involved in sending deadly explosives into Iraq but acknowledged he didn't know whether top Iranian leaders were responsible.

"What we do know is that the Quds Force was instrumental in providing these deadly IEDs to networks inside of Iraq," Bush said at a White House news conference, referring to a branch of the Iranian Revolutionary Guard.

"We also know that the Quds Force is a part of the Iranian government."

Bush insisted there was no contradiction between statements from his administration and the U.S. military.

"I don't think we know who picked up the phone and said, 'The Quds Force, go do this,' but we know it's a vital part of the Iranian government. What matters is, is that we're responding."

The possible involvement of the Iranian government in sending weapons to Iraq has been a hot topic since unnamed military officials told journalists Sunday in Baghdad that Iran's Quds Force was providing munitions to Shiite groups in Iraq. (Full story)

The briefers said the Quds Forces answer directly to Iran's supreme leader, Ayatollah Ali Khamenei, and that orders for their operations come "from the highest levels of the government."

The officials displayed evidence of the armor-piercing explosives found in Iraq and said they have caused 170 coalition deaths. (Read Time.com's analysis on how much Iran is to blame for Iraq)

The weekend briefing generated much controversy, with bloggers, journalists and others questioning whether the military was trying to drum up public sentiment for a confrontation with Iran.

There was also criticism that the briefers wouldn't allow reporters to use their names.

But the president Wednesday rejected as "preposterous" suggestions that the United States was creating a basis for conflict with Iran.

"My job is to protect our troops, and when we find devices that are in that country that are hurting our troops, we're going to do something about it, pure and simple.," he said "... Does this mean you're trying to have a pretext for war? No. It means I'm trying to protect our troops. That's what that means."

On Tuesday, Gen. Peter Pace, chairman of the Joint Chiefs of Staff, did not go as far as assertions made during Sunday's briefing in Baghdad.

During a trip to Australia, Pace told Voice of America, "It is clear that Iranians are involved and it is clear that materials from Iran are involved, but I would not say, based on what I know, that the Iranian government clearly knows or is complicit." (Full story)

Also Wednesday, a U.S. military spokesman in Baghdad would not confirm recent military statements that Iran's leadership is directing the production of an armor-piercing explosive said to be supplied to extremists in Iraq.

"I think people want to make an inference," Maj. Gen. William Caldwell said at a briefing. "I think people want to hype this up. What we're saying is that in Iran ... munitions are being manufactured that are ending up in Iraq. We are asking the Iranian government for that to stop. It all boils down to that."

Caldwell said there was a "tremendous amount of agreement" between Pace's remarks and what other military officials are saying. He cited physical evidence of Iran munitions, the manufacturing of the explosively formed penetrators, known as EFPs, and the detention of Quds Force personnel. (Watch Pentagon top brass discuss the possible Iran connection )