DEFIANCE

The last-ditch bid from Brussels came as uncertainty built ahead of Sunday's referendum, with a string of European leaders warning that it would effectively be a choice between remaining in the euro or reverting to the drachma.

Opinion polls show Greeks in favour of holding on to the euro but a rally of tens of thousands of anti-austerity protestors in Athens on Monday highlighted the defiance many in Greece feel about being pushed into a corner by the lenders.

Further rallies are expected in coming days, with a demonstration in favour of staying in the euro planned in central Athens on Tuesday.

Tsipras broke off negotiations with the Commission, the IMF and the European Central Bank and announced the referendum on the bailout terms early on Saturday, giving voters just one week to debate the fundamental issues at stake.

Under Juncker's offer, Tsipras had 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.

European Union leaders hammered home the message that the real choice facing Greeks is whether to stay in the euro zone or return to the drachma, even though the EU has no legal way of forcing a member state to leave the single currency.

Italian Prime Minister Matteo Renzi warned against turning the referendum into a personality contest between Tsipras and Juncker or Merkel.

"This is not a referendum on European leaders. This is a run-off vote: euro or drachma," Renzi told the Italian business daily Il Sole 24 Ore.

"The Greeks do not have to say whether they love their prime minister or the head of the European Commission more. They have to say whether they want to stay in the single currency."