The eurozone has said only six working days are left for Greece to come up with a revised list of reforms to seal a deal on its next rescue bailout.
Eurozone deputy finance ministers want an agreement on the €7.2bn loan in time for a Eurogroup meeting on 24 April.
An EU official said: “If you take into account weekends and Orthodox Easter, there are only six days left.”
It comes as Greece promised to meet Thursday’s deadline to repay €460m to the International Monetary Fund.
A Greek government official told the Reuters news agency that the payment to the IMF would go ahead on Thursday.
“The payment has been scheduled and will go out later today,” the official said.
Other, much larger, debt repayments are due within a few weeks.
Greek prime minister Alexis Tsipras has said that Athens will not be able to service its debt without financial help from the European Union.
Without new money it will struggle to renew €2.4bn in treasury bonds due to mature in the middle of April, or pay back another €0.8m to the IMF on 12 May.
It also has to find the funds to pay wages and pensions.
Since winning the elections in January on a mandate of ending austerity measures, Mr Tsipras’ government has been locked in negotiations with its creditors to ease the conditions of the loans.
Last month, the Financial Times reported that the country was using reserves from its health service and state owned utilities to pay off debts.
Mr Tsipras met Russian President Vladimir Putin this week in Moscow, but Mr Putin said he did not ask for financial aid from Russia during their talks.