European Commission President Jean-Claude Juncker said Friday he was "quite sure" the EU and Britain would reach a deal at a summit in February on reforms that London has demanded to stay in the bloc.
"I am quite sure that we'll have a deal -- not a compromise, a solution, a permanent solution -- in February," Juncker, the head of the executive branch of the 28-nation union, told a press conference.
"I am neither optimistic nor pessimistic. I know that we have to deliver," adding that "my knowledge" allowed him to be confident of a deal.
But Juncker warned that all of the demands by British Prime Minister David Cameron -- who is set to hold a referendum later this year on his country's membership of the European Union -- would be tough to reach agreement on.
"The issues put on the table by the British prime minister are all difficult issues," said Juncker, a former Luxembourg premier.
"Don't think there is one issue which would be particularly difficult - although it is and that's the welfare issue -- and that the other points mentioned by the British will be less important, and easy. They are not," he said.
"Even ever-closer union, the role of national parliaments, the relations between the ins and the outs in the euro system, all these are very, very difficult issues and we have to work hard in thiese days to come to agreements."
Cameron's most controversial proposal is a four-year ban on top-up benefits for EU migrants working in Britain, which critics say is discriminatory and threatens freedom of movement in the EU.
He also wants the EU to give Britain safeguards against more political integration, to protect countries that do not use the euro currency and to boost economic competitiveness.