"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.

The assurance to Iran's leaders was Bush's bluntest assessment yet. Last week, he used a series of pre-trip interviews with European journalists to minimize talk of any military attack by the United States.

Bush has walked a careful line between supporting an approach led by European nations to persuade Iran to scrap its uranium enrichment program in exchange for technological, financial and political support without talking about the U.S. reservations about that strategy.

"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 toward incentives, insisting that Tehran abandon its program.

The possibility of a military strike has been raised since the U.S.-led war with Iraq (news - web sites) over its alleged weapons of mass destruction, which never were found.

Also on Tuesday, Bush hailed NATO's modest pledge to help train security forces in Iraq, saying "every contribution helps."

"The NATO 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 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."

Bush also reiterated U.S. opposition to Europe's plans to lift its 15-year arms embargo against China. Bush said the United States fears that removing the ban would upset the balance in the Asian region.

"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