Greece and its creditors have launched a new round of talks in Brussels in a fresh bid to unlock billions of euros in loans and save the country from bankruptcy.
Prime minister Alexis Tsipras met representatives of the main lending institutions, under pressure to seal an agreement before facing other European Union leaders at a summit later.
Technical experts are sifting through Greece's latest offer of far-reaching reforms in exchange for debt relief, days before Athens is scheduled to make yet another repayment to the International Monetary Fund.
Mr Tsipras is also under massive pressure domestically as the compromises suggested so far will mean new hardship for citizens already suffering the impact of past austerity measures to bring public spending back into line.
Representatives from almost every Greek party were in Brussels, following developments blow by blow, to see whether they would be able to back any new deal in the Greek parliament, where a vote must pass by Monday.
"We are at a critical moment," labour minister Panos Skourletis warned on Antenna television.
"There are issues that for us are paramount, that must be included in an agreement. These are tackling the debt so that it can go on a sustainable course, and the financing of the economy," he said.
A senior policymaker in Mr Tsipras's radical left governing party denounced the international demands for new spending cuts as "blackmail".
"The effort to restore exhausting measures shows the blackmail and pressure against Greece is culminating," Syriza party parliamentary spokesman Nikos Filis said on Mega television.
Greece has a €1.6 billion debt to pay on Tuesday which it cannot afford unless the creditors unfreeze €7.2 billion in bailout money.
A failure to reach agreement with creditors and a default on its debts could force Greece out of the eurozone, which would be hugely painful for the country. Some experts say it could be manageable for Europe and the world economy, but that remains unclear and any failure would shake world markets.
The European Central Bank has approved a request from Athens to increase the amount of emergency liquidity Greek lenders can tap from the country's central bank, a Greek banking official said.
The ECB approved the request today, as it has done every day since Friday.
Worried Greeks have been withdrawing their money from their country's banks, fearing the imposition of restrictions on banking transactions. An estimated more than €4 billion left Greek banks last week.