Greek riot police have fired tear gas at protesters in violent clashes close to a key European Union summit in Athens.
Petrol bombs were thrown at police
Reporters said some of the demonstrators threw petrol bombs and red paint at police, after breaking away from a large anti-war protest.
At the summit, all 15 EU states and the 10 new members formally signed a treaty setting in stone the EU's historic eastward expansion.
The 10 newcomers will formally join in May 2004.
But the summit has been overshadowed by the EU's bitter splits over Iraq, which have divided leaders as well as sparking public anger.
The clashes happened in Athens' Syntagma Square, only 300 metres (yards) from the hall where leaders have been meeting.
Reports said a bank had also been set on fire, shop windows smashed, and petrol bombs and other missiles thrown at the UK and Italian embassies.
There is smoke from Molotov cocktails and tear gas billowing
in the air
"There is smoke from Molotov cocktails and tear gas billowing in the air," said Reuters reporter Karolos Grohmann, who witnessed the clashes.
Dozens of protesters were said to have occupied the Athens offices of British Airways, where they erected a large banner reading "Killers, imperialists".
Ten thousand police officers are believed to be involved in the security operation at the summit.
A banner was unfurled at the British Airways building
On his way to Athens, UK Prime Minister Tony Blair visited the German Chancellor Gerhard Schroeder - one of Europe's most committed war opponents - in what was seen as a bridge-building mission.
Most EU leaders are thought to be keen to move on from their bitter pre-war splits, and at least agree on how to run and rebuild Iraq after the conflict.
Crucially, they will have to agree on what role the UN should have.
United Nations Secretary General Kofi Annan, also attending the two-day summit, will consult key members of the UN Security Council on their views on a future role for the UN in Iraq.
The last few months have shown just how difficult it will be to turn rhetoric about a unified Europe and a common foreign policy into reality, says BBC Europe correspondent Chris Morris.
We must do everything... to reinforce the transatlantic dialogue and avoid any worsening of relations between Europe and
the United States
Greek Prime Minister Costas Simitis
UK Prime Minister Tony Blair has called on his European allies to put their differences over the war in Iraq behind them and concentrate instead on finding agreement over the best way to reconstruct the country.
Greek Prime Minister Costas Simitis, whose country holds the rotating EU presidency, also urged European leaders to find some ground for unity.
"We must do everything... to reinforce the transatlantic dialogue and avoid any worsening of relations between Europe and
the United States," he said on Tuesday.
"In the long term, nobody can govern the world alone."
Police have kept protesters back from summit venue
But there are still strong disagreements over how Iraq should be reconstructed, both economically and politically.
French President Jacques Chirac and Mr Schroeder have both made clear they expect the UN to play a high-profile, central role, covering humanitarian assistance as well as offering some form of political input.
But the United States, which led the military intervention in Iraq, believes it should decide largely how any post-conflict administration is shaped.
While Mr Blair is closely allied to the United States on Iraq policy, he is known to be more enthusiastic than many in Washington about a wider role for the UN.