Greece has until the end of Thursday to present new proposals to secure a third bailout from creditors and prevent a possible exit from the eurozone.
Prime Minister Alexis Tsipras says the “next hours will be crucial”.
His cabinet is meeting to discuss the plans which need to be submitted to Greece’s creditors by 22:00 GMT on Thursday.
The new proposals will be studied by eurozone finance ministers on Saturday and a full EU summit on Sunday.
The Greek government has meanwhile extended bank closures and the €60 (£43; $66) daily limit on cash machine withdrawals until Monday.
The curbs were imposed on 28 June, after a deadlock in bailout talks with creditors led to a rush of withdrawals.
Louka Katseli, the head of the Greek bank association, said on Thursday that there was enough liquidity in cash machines to serve the public until Monday.
The German Chancellor Angela Merkel said that “a classic haircut” (meaning reducing the value of Greece’s debts) was “out of the question” for her.