Disagreements over the conflict are likely to overshadow proceedings inside the meeting too, where the heads of all 15 European Union members are meeting to formally welcome 10 more nations -- mainly from central and eastern Europe.

The street violence erupted after hundreds of demonstrators attempted to break through police lines in Syntagma Square, hundreds of meters from the EU summit, news agencies reported.

Police fired tear gas into the crowd after protesters set fire to bank buildings and smashed the windows of stores and vehicles.

Demonstrators also threw rocks, bottles of paint and petrol bombs at the Italian, French and British embassies, Reuters said. Clashes were also reported in front of the U.S. Embassy. Britain and Italy backed the U.S.-led war against Iraq but France was staunchly against military action.

Police said about 8,000 protesters were involved in the clashes. About 50 demonstrators were detained and at least five people were injured, Reuters reported.

Tight security had been put in place in an effort to seal off politicians from the demonstrations. About 20,000 police officers are on duty for the two-day meeting.

Differences exist within the conference room with those in the EU who had opposed the war lining up alongside those who were for it.

French President Jacques Chirac had become embroiled in a public discussion before the war with candidate countries which backed U.S. President George W. Bush.

Wednesday's clashes in Syntagma Square followed earlier protests in the city when about 100 demonstrators took over a British Airways office in a southern suburb to protest against the presence of UK Prime Minister Tony Blair. The British leader had been Bush's staunchest ally.

The war has divided the continent like no other issue in recent decades and has highlighted what the United States has called a divergence between "old" and "new" Europe -- in other words, those opposed to the war and others, mostly ex-communist countries, that backed the U.S. campaign.

U.S. Defense Secretary Donald Rumsfeld castigated the anti-war camp by saying: "You're thinking of Europe as Germany and France. I don't. I think that's old Europe."

Chirac was equally dismissive of pro-war countries, saying they were "badly brought up" and that they had "missed a good opportunity to shut up."

But many see this week's summit as an opportunity to resolve the disputes and move on.

"This is a kiss-and-make-up summit," Theodorous Kouloumbis, head of the Hellenic Foundation for Defense and Foreign Policy, told Reuters.

Greece, which holds the EU's rotating presidency, left Iraq off the official agenda on Wednesday, when the leaders of the 10 new members -- Cyprus, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia -- are due to sign an accession treaty.

The 10 will join the EU in May 2004, once all existing members have approved the enlargement process and each of the applicant countries have held referendums.

Michalis Tsinisizelis, professor of politics at Athens University, added: "I think EU members will grab this opportunity to reflect a new unity among them after such a turbulent time."