EU President Donald Tusk told Britain on Wednesday that it needed to rethink its negotiating position on the Irish border and on future trade ties with the European Union as part of Brexit negotiations.
Speaking ahead of an EU summit in Salzburg, Tusk welcomed some of Prime Minister Theresa May's proposals but warned that on "other issues such as the Irish question, or the framework for economic cooperation, the UK's proposals will need to be reworked".
Both sides had hoped to strike a Brexit deal at an October EU summit, to allow time for its ratification by the British and European parliaments before Britain's departure from the bloc in March 2019.
But Tusk repeated his proposal for another special summit in mid-November to seal the agreement.
"Today there is maybe more hope, but there is surely less and less time," he said.
"The Brexit negotiations are entering the decisive phase," Tusk said, adding that "various scenarios are still possible today".
He welcomed Britain's "readiness to cooperate globally in the area of security and foreign policy".