But those hopes were quickly dashed.

German Chancellor Angela Merkel said she ruled out further negotiations with Greece before Sunday's popular vote on whether to accept creditors' demands for budget reforms.

"Before the planned referendum is carried out, we will not negotiate over anything new," the dpa news agency quoted Merkel as saying.

Greece's latest offer involves a proposal to tap Europe's bailout fund _ the so-called European Stability Mechanism, a pot of money set up after Greece's rescue programs to help countries in need.

Tsipras' office said the proposal was "for the full coverage of (Greece's) financing needs with the simultaneous restructuring of the debt."

Dijsselbloem said the finance ministers would "study that request as we should" and that they would hold another conference call Wednesday, as they had also received a second letter from Athens that they had not had time to read.

Dragasakis said the new letter "narrows the differences further."

"We are making an additional effort. There are six points where this effort can be made. I don't want to get into specifics. But it includes pensions and labor issues," he said.

European officials and Greek opposition parties have been adamant that a "No" vote on Sunday will mean Greece will leave the euro and possibly even the EU.

The government says this is scaremongering, and that a rejection of creditor demands will mean the country is in a better negotiating position.

In Athens, more than 10,000 "Yes" vote supporters gathered outside parliament despite a thunderstorm, chanting ``Europe! Europe!''

Most huddled under umbrellas, including Athens resident Sofia Matthaiou.

"I don't know if we'll get a deal. But we have to press them to see reason," she said, referring to the government. "The creditors need to water down their positions, too."

The protest came a day after thousands of government supporters advocating a "No" vote held a similar demonstration.

On Monday, European Commission President Jean-Claude Juncker made a new offer to Greece. Under that proposal, Tsipras would need to accept the creditors' proposal that was on the table last weekend. He would also have to change his position on Sunday's referendum.

Commission spokesman Margaritis Schinas said the offer would also involve unspecified discussions on Athens's massive debt load of over 300 billion euros, or around 180 percent of GDP. The Greek side has long called for debt relief, saying its mountainous debt is unsustainable.

A Greek government official said Tsipras had spoken earlier in the day with Juncker, European Central Bank chief Mario Draghi and European Parliament president Martin Schulz.

Meanwhile, missing the IMF payment will cut Greece off from new loans from the organization.

And with its bailout program expiring, Greece will lose access to more than 16 billion euros ($18 billion) in financial support it has not yet tapped, officials said. They spoke on condition of anonymity because talks about the program were still ongoing.

On the streets of Athens, long lines formed again at ATM machines as Greeks struggled with the new restrictions on banking transactions. Under credit controls imposed Monday, Greeks are now limited to ATM withdrawals of 60 euros ($67) a day and cannot send money abroad or make international payments without special permission.

The elderly have been hit particularly hard, with tens of thousands of pensions unpaid as of Tuesday afternoon. Many also found themselves completely cut off from any cash as they do not have bank cards.

The finance ministry said it would open about 1,000 bank branches across the country for three days beginning Wednesday to allow pensioners without bank cards to make withdrawals. But the limit would be set at 120 euros for the whole week.