"I can say with certainty that the Quds Force, a part of the Iranian government, has provided these sophisticated IEDs (improvised explosive devices) that have harmed our troops," Mr. Bush said at his White House news conference of the year.
"Whether Ahmadinejad (Iran's president) ordered the Quds force to do this, I don't think we know. But we do know that they're there, and I intend to do something about it," Mr. Bush continued.
The president was quick to say he isn't talking about attacking or invading Iran, reports CBS News chief White House correspondent Jim Axelrod, but he said he has no doubts that Iran is sending bombs and other weapons into Iraq.
"To say it is provoking Iran is just a wrong way to characterize the commander in chief's decision to do what is necessary to protect our soldiers in harm's way," Mr. Bush said.
The tough talk may have the opposite effect, reports Axelrod.
"What it's likely to do is not to get the Iranians to back away, but rather tempt them to show us they can't be pushed around," says Middle East expert Martin Indyk of the Saban Center for Middle East Policy and the Brookings Institution.
Democratic presidential candidatenot to take any military action against Iran without getting congressional approval.
"If the administration believes that any, any use of force against Iran is necessary, the president must come to Congress to seek that authority," Clinton, a member of the Armed Services Committee, said in a Senate speech.
Meanwhile, Mr. Bush shrugged off congressional debate on a resolution opposing his Iraq policy, noting that the measure was nonbinding and mostly symbolic. But he said U.S. troops are counting on lawmakers to provide them the funds they need to win.
Mr. Bush spoke as the Democratic-controlled House of Representatives debated a measure opposing his decision to send some 21,500 additional troops to Iraq.
"They have every right to express their opinion, and it is a nonbinding resolution," he said of the House members. But he suggested he would dig in his heels if Congress wavered on emergency spending legislation to pay for the operation.
"Our troops are counting on their elected leaders in Washington, D.C. to provide them with the support they need to do their mission," Mr. Bush said.
In his first news conference since Dec. 20, the president said he had just received his first briefing from Baghdad by Gen. David Petraeus, the new chief commander of U.S. forces in Iraq.
Mr. Bush said he talked with Petraeus about coordination between Iraqi and coalition forces, and that while it seemed to be good, more work was needed on developing an efficient command-and-control structure.
Meanwhile, Mr. Bush responded carefully when asked about Russian President Vladimir Putin's recent sharp criticism. He has a "complicated relationship" with the Russian leader, the president said.
Putin slammed U.S. domination of world affairs at an international conference of security officials in Germany over the weekend, saying the U.S. was making the world more dangerous by overusing its military power.
The depth of Putin's criticism surprised U.S. officials. Moscow and Washington drew closer together immediately after the Sept. 11, 2001, terror attacks, but more recently relations have been strained.
Mr. Bush emphasized he and Putin have a lot they agree on, including on making sure that Iran does not develop nuclear weapons.
The president also put the spotlight on the tentative nuclear deal with North Korea, CBS News correspondent Aleen Sirgany reports. The communist country agreed this week to halt its atomic program in exchange for oil.
"This is a good first step. There's a lot of work to be done to make sure the commitments made in this agreement become reality," he said.
On no issue was the president more emphatic than his refusal to discuss anything connected to the Lewis "Scooter" Libby trial. Three times he shut down a reporter who asked about the perjury trial of Libby, a former vice presidential chief of staff.
"Would you like to think of another question? Being the kind man that I am, I will recycle you," he told the reporter, drawing laughter.
Mr. Bush also served notice that he won't be commenting on the candidates running for his job. "I will resist all temptation to become the pundit-in-chief," he said.
On alleged Iranian involvement in Iraq, Mr. Bush appeared to back away from assertions at a weekend briefing in Baghdad by three senior U.S. military officials.
The officials said shipments into Iraq of deadly new weapons and technology had been approved at the highest levels in Tehran.
Mr. Bush said that he could only say "with certainty" that the weapons were provided by an elite part of Iran's Revolutionary Guards, which is part of the government.
But, the president added, he does not know whether the weapons were "ordered from the top echelons of government. But, my point is, what's worse, them ordering it and it happening, or them not ordering it and it happening?"
Mr. Bush spoke a day after Gen. Peter Pace, chairman of the Joint Chiefs of Staff, cast doubts on the claims that higher-ups in the Iranian government had authorized the arming of Iraqi Shiite militias. Pace told reporters that materials used in some of the munitions could be traced to Iran, "but that does not translate that the Iranian government per se, for sure, is directly involved in doing this."
It is a sensitive issue, since the administration has been accused by its critics of basing the invasion of Iraq on faulty intelligence.