WASHINGTON, Feb. 14 -- President Bush said today he is certain that elements of the Iranian government are supplying deadly roadside bombs that kill American troops in Iraq, even if the innermost circle of the government is not involved.

Mr. Bush said it had been established beyond a doubt that a branch of the Iranian Revolutionary Guard Corps known as the Quds Force is supplying Shiite groups inside Iraq with particularly deadly, Iranian-designed weapons known as explosively formed penetrators, or E.F.P.s.

“We know that,” Mr. Bush said at a White House news conference.

The United States regards the Quds Force as part of the Iranian government, since the force has historically been under the command of Iran’s senior religious leaders. And even if the highest officials in Tehran have not directly ordered the Quds Force to supply weapons to Iraqi Shiites, they are still complicit, Mr. Bush said.

“What’s worse?” Mr. Bush asked. “That the government knew, or that the government didn’t know?”

The weapons include squat canisters designed to explode and spit out molten balls of copper that cut through armor. The canisters are perhaps the most feared weapon faced by American and Iraqi troops, and American military leaders say they have killed more than 170 United States soldiers in the past three years.