Greece will not be able to pay the International Monetary Fund on June 5 unless foreign lenders disburse more aid to the debt-ridden country.
EU paymaster Germany criticised the Greek proposal as "not a substantial solution" as it failed to fulfil bailout conditions.
Day two of protests in Greece have seen demonstrators march to Parliament against austerity measures required by the IMF and the European Union.
Greek police with teargas and batons fought hooded youths near Parliament on Tuesday as violence broke out at a rally against anti-austerity measures.
Greeks raged against a wave of austerity on Wednesday after finance ministers failed to agree how to make private creditors contribute to a bailout.
Protesters clashed with police and set fire to cars and a hotel in Athens on Wednesday as tens of thousands marched against austerity measures.
Greece's economic crisis sent shivers of fear through global markets on Thursday over concern it could spread like wildfire through Europe and beyond.