EU leaders have signed a Charter of Fundamental Rights in a show of unity at the start of a summit expected to see bitter wrangling over controversial institutional changes.

The Charter lays down civil, political, economic and social rights for citizens of EU countries, but will not be included in the treaty that it is hoped will be agreed at the summit in Nice.

The main purpose of the summit is to pave the way for enlargement of the EU from the present 15 member states to a total of 25 or more.

Prodi: Urges speedy enlargement

At a pre-summit meeting with leaders of 13 countries that are candidates to join the EU, European Commission President Romano Prodi called for a speedy conclusion to the enlargement talks.

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

As the meeting got under way on Thursday , police fired tear gas at protesters outside the main conference centre in Nice, where the summit is being held.

Demonstrations that began peacefully slipped out of control, as groups of protesters hurled stones and bottles at riot police, who responded with rounds of tear gas.

A bank in a street close to the conference centre was briefly set alight.

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

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

The demonstrators are from a number of groups, including anarchists and anti-capitalists. Some condemned the Charter of Fundamental Rights, saying that it would not encourage higher standards of living and only offers a minimum level of rights.

Mr Chirac condemned the violence, which he said was "contrary to democratic principles".

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 new members.

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

Correspondents say there is a real risk of failure.

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.

Protesters vent their anger at the talks

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.