EU Council president Donald Tusk says the talks on reforming the bloc are at a "critical" stage
EU Council president Donald Tusk says the talks on reforming the bloc are at a "critical" stage and there is a "real risk" that the EU could break up.
The politician tweeted his concerns after the latest in a series of meetings across the continent to win support for his proposals.
A draft text, based on reforms that British Prime Minister David Cameron wants to achieve, is to be discussed by 28 EU leaders at a summit on Thursday.
After negotiations in Romania, Mr Tusk said: "It will be a crucial summit with the two biggest challenges to the future of the European Union on the agenda: The United Kingdom's future membership of the European Union and the migration crisis.
"On neither can we afford to fail.
"At stake is the United Kingdom's membership of the EU. A question which only the British people can and will decide.
"At stake is also the future of our European Union where we will all have to decide together, and where we cannot and will not compromise on the fundamental freedoms and values."
He aded: "This is a critical moment.
"It is high time we started listening to each other's arguments more than to our own.
"The risk of break-up is real because this process is indeed very fragile. Handle with care. What is broken cannot be mended."
Mr Cameron has agreed to hold an emergency Cabinet meeting on Friday if he secures an EU deal at the Brussels summit, Sky News say.
The PM has offered to talk to any Cabinet colleagues who may have questions over his EU renegotiation efforts.
Sky News report that several ministers in Cameron's Cabinet have reservations.
The meeting will see the suspension of "collective responsibility", so members of the Cabinet will be free to express their views and support either the "leave" or "remain" campaigns in a referendum on Britain's membership of the EU likely to take place in June.
Before that the PM needs to get a deal done.
He has arrived in Paris for talks with French President Francois Hollande.
He then goes to Brussels on Tuesday to meet European Parliament president Martin Schulz and three MEPs who have been appointed "sherpas" for the renegotiations.
He will then meet leaders of the Socialist and EPP groupings.
Asked whether Mr Cameron was confident of securing a deal, a spokeswoman said: "We have made progress but there are details to be pinned down.
"Nothing is agreed until everything is agreed."