"This notion that the United States is getting ready to attack Iran is simply ridiculous. Having said that, all options are on the table," Bush said after discussing the issue with European allies.
Bush used his bluntest language yet to give assurance to Iran's leaders. Last week, in a series of pre-trip interviews with European journalists, he also tried to dispel talk of a military attack, an issue that has been raised repeatedly since the United States went to war with Iraq primarily over its alleged weapons of mass destruction. No such weapons have been found in Iraq.
On Iran, Bush has walked a careful line in expressing support for a European-led approach offering Iran technological, financial and political support in return for scrapping its uranium enrichment program.
"It's in our interests for them not to have a nuclear weapon," Bush said in a news conference with European Union leaders.
The United States has refused to get involved in the bargaining with Tehran or to make commitments about incentives, insisting that Tehran abandon its program.
Also on Tuesday, Bush hailed NATO's modest pledge to help train security forces in Iraq, saying "every contribution helps."
"The NATO (search) training mission is an important mission, because after all, the success of Iraq depends upon the capacity and the willingness of the Iraqis to defend their own selves against terrorists," he said during an earlier news conference at NATO headquarters.
Bush also made clear his intention to challenge Russian President Vladimir Putin (search) on recent actions, including restrictions on the press and Moscow's treatment of neighboring Baltic countries, that U.S. officials view as harmful to democracy there. The two leaders meet Thursday in Slovakia.
"A constructive relationship allows me to remind him that I believe Russia is a European country and European countries embrace those very same values that America embraces," Bush said. "I'm confident that can be done in a cordial way."
Putin defended his approach.
"Russia chose democracy 14 years ago not to please anyone, but for its own sake, for the sake of the nation and its citizens," Putin said. "Naturally, basic principles and institutions of democracy must be adapted to today's realities of Russian life, to our traditions and history."
Bush also reiterated U.S. opposition to Europe's plans to lift its 15-year arms embargo against China.
"There is deep concern in our country that a transfer of weapons will be a transfer of technology, that it will change the balance of relations between China and Taiwan," Bush said.
He said he understands that the Europeans are working on a way to address U.S. worries about allowing China to modernize its military with arms and communications, intelligence and surveillance equipment that would give Beijing an edge over Taiwan.
"They know the Congress is concerned," Bush said. "And so they'll try to develop a plan that will ease concerns. Now, whether they can or not, we'll see."
But French President Jacques Chirac (search), while stressing that security guarantees could be worked out, indicated that Europe remains steadfast in its desire to end the ban. "We intend to lift the last obstacles in our relations (with China), and this within a spirit of responsibility," he said.
In Beijing on Tuesday, Chinese Foreign Ministry spokesman Kong Quan said that abolishing the "erroneous and outdated measure" would help move forward China-EU relations.
As Bush shuttled in between NATO headquarters and meeting with European Union leaders, opposition to the U.S. president was evident in the streets of Brussels as protesters lobbed a fire bomb at riot police. Police responded with water cannons to disperse the crowd that they estimated was 1,000 strong.
Police said they did not know if anyone was injured. Associated Press Television News reporters saw several people arrested.
On Iraq, Luxembourg Prime Minister Jean-Claude Juncker, whose country holds the rotating European Union presidency, said the United States and the EU will host a conference to rally international support for Iraq if the new government there requests it.
NATO, meanwhile, succeeded after struggling for months to get a commitment from all allies to join the mission in Iraq, including those that vigorously opposed the U.S.-led war there.
"All 26 allies are working together to respond to the Iraqi government's request for support by training Iraqi security forces, providing equipment and helping to fund NATO's efforts," Jaap de Hoop Scheffer told the NATO summit.
The development of a reliable Iraqi security force, so that Iraqis can handle their own security, is considered vital to lowering the U.S. troop presence there. Army Lt. Gen. David Petraeus, the general in charge of training Iraqi troops, has said that about 136,000 Iraqis have been trained and equipped - fewer than half the ultimate goal of a force of about 270,000.
The NATO mission comprises just over 100 instructors training senior Iraqi officers in Baghdad's heavily protected "Green Zone" — more than half of them American.
Alliance planners hope to expand that operation to 160 instructors. In September, they hope for NATO to help run a military academy outside the Iraqi capital - if it can find the troops and money needed.
Bush said the assistance is more than a mere gesture designed to symbolize the end to bitter divisions wrought by the war. "Twenty-six nations sat around the table saying, you know, 'Let's get the past behind us and now let's focus on helping this — the world's newest democracy — succeed,'" Bush said.
However, in a sign of lingering differences, France, Germany and other opponents of the war will not send instructors to Iraq, limiting their contribution to training outside the country or funding for the operation.
Earlier Tuesday, Bush met with British Prime Minister Tony Blair, Italian Premier Silvio Berlusconi and Viktor Yushchenko, the new, Westward-leaning president of Ukraine. Yushchenko, is the only non-alliance leader invited to the NATO summit, has said that withdrawing Ukraine's 1,600 troops from Iraq is topping the agenda for his country's cash-starved military.