The head of the European Commission made a last-minute offer to try to persuade Greek Prime Minister Alexis Tsipras to accept a bailout deal he has rejected before a referendum on Sunday which EU partners say will be a choice of whether to stay in the euro.


But Greek government sources said the leftist premier stood by his rejection of the creditors' conditions and Greece would default on a crucial repayment due to the International Monetary Fund on Tuesday, plunging it deeper into financial crisis.


EU and Greek government sources said Jean-Claude Juncker had offered to convene an emergency meeting of euro zone finance ministers on Tuesday to approve an aid payment to prevent Athens defaulting, if Tsipras sent a written acceptance of the terms.


He also dangled the prospect of a negotiation on debt rescheduling later this year if Athens said "yes'.


The last-ditch bid from Brussels came after tens of thousands of Greeks, mobilised by Tsipras' Syriza party, demonstrated in Athens against further austerity.


Tsipras broke off negotiations with the Commission, the IMF and the European Central Bank and announced early on Saturday a referendum on the bailout terms next Sunday, giving voters just one week to debate the fundamental issues at stake. Under Juncker's offer, Tsipras would have to send a written acceptance by Tuesday of the terms published by the EU executive on Sunday and agree to campaign in favour of the bailout in the planned July 5 referendum.