Donald Tusk, President of the European Council, says it will be "very, very tough" to reach an EU reform deal with Britain.

Speaking at a news conference following an EU summit in Malta, Mr Tusk said that there was "no guarantee" of an agreement in December, when the region's leaders are next due to meet.

He described British requests, set out by British Prime Minister David Cameron in a six-page letter just days ago, as tough, adding: "I have to say that it will be really difficult to find an agreement."

Mr Cameron had said in the letter that he was "ready to campaign with all my heart and soul to keep Britain inside a reformed European Union" if an agreement can be reached.

One of the sticking points is Mr Cameron's bid to ban EU migrants to the UK from claiming benefits for the first four years of their stay, something that the European Commission has described as "direct discrimination between EU citizens".

The ban is an effort by Mr Cameron to end what he describes as the attraction of Britain's generous welfare system.

He hopes to reach an agreement on economic reform, cutting red tape and a host of other changes, by the end of this year.

A referendum on Britain's membership of the 28-nation bloc has been promised before the end of 2017.