By DPA
Brussels : The European Union (EU) will continue talks on a new treaty Friday but success in clinching agreement could still prove elusive, German Chancellor Angela Merkel has warned.
Merkel said late Thursday that all leaders had shown a willingness to negotiate on details of the deal. "Nobody said 'I do not want to reach agreement'."
The atmosphere during four hours of intensive discussions among leaders had been one of "mutual understanding", said Merkel.
But she warned that success was not guaranteed.
Merkel is chairing the EU summit called to clinch a new "reform" treaty to replace an earlier draft constitution rejected by French and Dutch voters in 2005. Germany is the current president of the 27-nation EU.
The German leader said EU officials would work through the night to try and find common ground.
Urging compromise, Merkel said "people in Europe and all over the world expect us to bring this to a fruitful conclusion".
EU leaders will spend perhaps Saturday as well in talks aimed at defining the outlines of the new treaty.
But signalling hours of hard bargaining ahead, outgoing British Prime Minister Tony Blair insisted he would not tone down key demands for changes in the treaty proposals drawn up Merkel.
"This is going to be a very tough negotiation," Blair said as he came into the meeting.
Britain was sticking to demands for "significant change" in four areas, Blair said, referring to London's opposition to the appointment of a first-ever EU foreign minister, refusal to accept a legally binding charter for fundamental rights, and demands for opt-outs in justice and police affairs.
"We need to be satisfied in full," Blair insisted.
However, Luxembourg's Prime Minister Jean-Claude Juncker, a backer of the original draft constitution, said he would not agree to a treaty that "lacks substance".
Polish President Lech Kaczynski made no comments as he greeted Merkel. But Poland's demand for an overhaul of EU voting rights has emerged as a major headache for Merkel's efforts to clinch a treaty deal at the summit.
Warsaw is opposed to the "double majority" system agreed in 2004 that requires that EU decisions have the support of 55 percent of member states, representing 65 percent of the population.
Instead, it wants a system based on the square root of each country's population, which will give more say to medium-sized nations compared with bigger EU states like Germany.
Seeking to ease tensions, Merkel insisted she would listen to all EU leaders.
"Each and every country will be taken seriously as regards its concerns. No country will be neglected," the German chancellor said.
The new treaty being discussed in Brussels makes no reference to EU symbols such as a European flag, anthem or "Europe Day" to avoid giving the impression leaders are working to create a European super state.
The treaty makes some concessions to Britain, including eliminating a reference to an EU foreign minister and giving countries the right to opt out of stronger co-operation on justice and police affairs.
The draft still includes plans to make the human rights charter legally binding, although it will make clear that this will not mean interference in national legislative procedures.
Merkel is hoping a deal in Brussels will allow a new EU treaty to be agreed under the Portuguese presidency by the end of the year, allowing for all 27 EU states to ratify the document ahead of elections to the European Parliament in summer 2009.