European Commission chief Jean-Claude Juncker insisted that Britain would not leave the EU, as leaders prepare to discuss David Cameron's reform demands at a summit next month.
Time was running out to get a desperately needed debt agreement in place after 10 hours of talks in Brussels, with Greece's economy and banking system at risk of imminent collapse.
Greek Foreign Minister Nikos Kotzias ruled out his country's exit from the EU and called for calm after Greek voters rejected bailout terms of international creditors.
French Prime Minister Manuel Valls sought to reassure Chinese concerns about the eurozone, insisting that Greece will stay part of the single currency.
French President Francois Hollande urged Greece to abide by its European commitments, as the spectre of a Greek exit from the eurozone rears its head again.