Bush said ahead of the landmark visit that his goal was "to seize the moment and invigorate a relationship that is a vital relationship for our own security, as well as a vital relationship for long-term peace in the world."

An unprecedented security operation locked down parts of the Belgian capital at the start of the three-country trip, which will also take him to Germany and Slovakia, where he will meet Russian President Vladimir Putin.

Bush has signalled that he will use their talks in Bratislava to challenge Putin on a series of decisions widely seen as setting back democracy in Russia.

Thousands of protestors are expected during the tour -- Bush's first foreign sortie since his second term began one month ago -- which includes summit meetings in Brussels Tuesday with NATO and European Union (EU) leaders.

Still widely unpopular in Europe, Bush was to preach reconciliation in a keynote speech on Monday and reinforce that message in bilateral meetings with several of the chief opponents of the March 2003 invasion of Iraq.

"I'll talk about a variety of areas where we can work together; talk about the greater Middle East, Middle Eastern peace and Iraq and Iran; talk about the need for us to work together to feed the hungry and take care of the diseased; I'll talk about the environment," the president said.

An early test will come Monday evening, when Bush hosts a peacemaking dinner for French President Jacques Chirac, who deeply angered Washington when he helped rally global opposition to the war in Iraq.

"But now is the time for us to set aside that difference and to move forward in areas where we can work together," on issues like Iran, the Mideast peace process, and ending Syria's presence in Lebanon, Bush said ahead of the trip.

Diplomats said that the EU would press the US leader for substantive progress on the Middle East "roadmap" following the election of a new Palestinian leadership and its declaration of a truce with Israel.

The 25-nation bloc was also expected to press Bush to ease his strident opposition to the International Criminal Court, which the United Nations wants to try suspects for crimes in Sudan's violence-wracked Darfur region.

Both sides have agreed to disagree on the mooted lifting of an EU embargo on arms sales to China and the Kyoto treaty on global warming, neither of which will be raised at the summit talks, EU sources said.

But one issue that Bush and his EU interlocutors cannot escape is Iran.

To allay fears that Iran seeks atomic weapons, Britain and its fellow EU heavyweights France and Germany have been negotiating with the Islamic republic to try to bring its nuclear activities into a regime of tough UN supervision.

US officials are pushing for Iran to be hauled before the UN Security Council. The Europeans prefer a carrot-and-stick approach coupling nuclear compliance with the promise of a lucrative new trade accord for Iran.

Bush said that talk of a US military strike on Iran's nuclear programs was "just not the truth," even as he has signalled mounting impatience with Tehran's response to the diplomatic overtures.

German Chancellor Gerhard Schroeder -- whom Bush will meet Wednesday in Mainz -- is set to ask the US president for diplomatic backing in the face-off with Iran.

Bush meanwhile is expected to push Schroeder for more help in training Iraqi security forces.

In a first sign of the public antipathy facing Bush in Europe, around 1,000 people demonstrated against his trip in central Brussels hours ahead of his arrival, brandishing signs including one reading "Bush is not welcome."

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