Athens has until the end of today to deliver new proposals to try to unblock more bailout cash from European creditors, Euronews reported.

"These are crucial times," said Alexis Tsipras, "and it is necessary to provide proper information to the political parties so that there are no misunderstandings."

As authorities extended the closure of Greek banks until next Monday, there was a stark warning that there is not enough cash to keep money machines in operation beyond the end of the week.

The leader of the To Potami party, Stavros Theodorakis, said, "We have to clinch an agreement before Sunday. It will be too late by Sunday. (It is crucial) to have reached a definite agreement by Friday morning."

The IMF warns that Greece is facing an "acute crisis", which needs to be addressed quickly. It says it remains engaged to help, but it cannot bend the rules.

IMF head Christine Lagarde said, "We have always advised that (rescue programs) walk on two legs, if you will. One leg is about significant reforms and fiscal consolidation and the other leg is debt restructuring, which we believe is needed in the particular case of Greece for it to have debt sustainability."

Details of Greece's new proposals, and how they are different to a plan rejected by the public in a referendum last weekend, are not yet known.

But one report says the latest reform ideas are more than what has been previously offered.