Protesters vent their anger at the talks

After earlier peaceful demonstrations, groups of protesters hurled stones and bottles at riot police, who responded with rounds of tear gas.

Demonstrators, many wearing gas masks, also set fire to a bank in a street close to the conference centre, although the fire was quickly extinguished.

Some 20 police were reported injured in clashes as they moved in to clear the area around the conference centre, where calm was returning by late morning. There were seven arrests.

The demonstrators are from a number of groups, including anarchists and anti-capitalists. Some are critical of the EU's plans for a Charter of Fundamental Rights - which will be proclaimed by the 15 current member states.

French President Jacques Chirac condemned the violence, which he said was "contrary to democratic principles".

On the agenda

Qualified majority voting on some issues Reweighting of votes to better reflect population Reducing numbers of European Commissioners Enhanced co-operation Better human rights monitoring Charter of Fundamental Rights BSE crisis EU and Nato co-operation

The EU leaders face a tough task over the next four days in agreeing a blueprint for the restructuring of the Union, to ease the admission of 12 or more new member states in the coming years.

Disputes over national interest threaten to prevent agreement being reached, with more than 300 hours of preparatory talks failing to break the deadlock.

At a meeting with leaders of 13 countries preparing to join the EU, European Commission President Romano Prodi urged a speedy conclusion for the enlargement talks.

His comments were echoed by Mr Chirac, who also spoke of the enlargement as the fulfilment of a dream of a more democratic Europe.

National interests

The summit aims to streamline the EU's institutions and voting procedures so that it can function efficiently with 27 members instead of the present 15.

But some countries fear that their interests might be eroded in the name of more efficient decision-making.

Prodi: Warned of the dangers of veto votes

The United Kingdom, in particular, feels that its veto over matters of taxation is under threat.

The size of the European Commission - the executive body of the union - will also be up for discussion. At present it is possible for each of the 15 member states to be represented on the commission.

But it is generally felt that if each of the 27 possible future states were to be represented on the commission, it would become unwieldy.

Franco-German tussle

The number of votes wielded by each country within the union is another point that is likely to prove contentious.

Council of Ministers votes

Germany, Britain, France, Italy - 10 Spain - 8 Belgium, Netherlands, Portugal, Greece - 5 Sweden, Austria - 4 Finland, Denmark, Ireland - 3 Luxembourg - 2

Germany wants a larger share of the votes, proportionate with being the most populous country in the union.

This has sparked a dispute between Germany and France - the two countries usually perceived as being at the core of the union.

A further point of discussion will be what is known as a "two-speed Europe" - the idea that states which favour closer integration can press ahead with forging ties among themselves, to the exclusion of those countries which want to preserve greater autonomy.

Plea for consensus

In the past few days, EU leaders have tried to send out the message that they favour consensus.

"Our competitors know they are dealing with a community where every member has a veto - and the opportunity is there for our rivals to play us off against each other," EU Commission President Romano Prodi wrote in an article in the UK newspaper The Guardian.

However, predictions are that discussions will continue until Sunday, with leaders debating late into the night over the wording of decisions that will allow the union's expansion plans to go ahead, without giving voters back home the impression that national interests are not being left behind.