ReutersGerman Chancellor Angela Merkel (left) and French President Francois HollandeEurozone leaders set Greece a Sunday deadline to come up with new and even-tougher economic measures if the country wants to avoid defaulting on the European Central Bank and crashing out of the currency union. As a sweetener for such a deal, leaders raised the possibility of some short-term financing to help Athens make a July 20 payment and — most important for Greek Prime Minister Alexis Tsipras — action down the road to relieve Greece’s crushing debt burden. Obstacles to an agreement that keeps Greece in the eurozone remain high, however. Most notably, the policy overhauls and budget cuts demanded go beyond those that were resoundingly rejected by Greek voters in a referendum last weekend. German Chancellor Angela Merkel said after Tuesday’s emergency summit of eurozone leaders that it is up to Greece to act. “Of course, at the very end, one will have to discuss how debt sustainability can be recreated but not by saying first ‘How do we close the gap?’ but “What can Greece do?’ ” she said. She added that Mario Draghi, the ECB president, made clear to leaders at the summit that Sunday would be “the right moment to take decisions” for Greece to avoid a meltdown of its banking system. Mr. Tsipras said that the negotiation process would be fast. “I believe there will be a solution by the end of the week at the latest,” he said. Nektaria Stamouli and Todd Buell contributed to this article