Greece delayed a key debt payment to the International Monetary Fund due yesterday as Prime Minister Alexis Tsipras, facing fury among his leftist supporters, demanded changes to tough terms from international creditors for aid to stave off bankruptcy.

The IMF said Athens had informed the global lender that it plans to bundle four payments due this month into a single €1.6 billion lump sum, which is now due on June 30.

“Under an Executive Board decision adopted in the late 1970s, country members can ask to bundle together multiple principal payments falling due in a calendar month,” IMF spokesman Gerry Rice said in a statement.

It was the first time in five years of crisis that Greece has postponed a repayment on its €240 billion bailouts from eurozone governments and the IMF, and it came as German Chancellor Angela Merkel said talks on a cash-for-reforms deal were still far from reaching an agreement.

Tsipras, elected in January on a promise to end austerity, yesterday returned from late-night talks with EU officials in Brussels to an outcry over conditions that would breach the “red lines” his Syriza party has declared.

He told ministers the government could not accept “extreme proposals” and said the creditors should understand that the Greek people had suffered enough and they “have to stop playing games at its expense”, a Greek official said.

The novice Prime Minister left the talks with European Commission President Jean-Claude Juncker and the chairman of eurozone finance ministers, Jeroen Dijsselbloem saying a deal with lenders was “within sight” and that Athens would make a €300 million payment to the IMF yesterday. His tone appeared to harden after he ran into a backlash in Athens.

Tsipras rejected pension cuts and a tax rise on electricity that he said the lenders were demanding

European officials continued to voice optimism that an agreement could be clinched in the coming days, but they acknowledged that large gaps remained to be bridged and said they expected Greek counter-proposals.

Tsipras rejected pension cuts and a tax rise on electricity that he said the lenders were demanding along with other conditions to win the release frozen loans and avert a default that could hit euro zone and world markets.

Sources familiar with the creditors’ five-page plan said it also asked Athens to commit to selling off state assets and maintaining unpopular labour reforms — demands that would cross the declared red lines.

The lenders were demanding that Greece reduce spending on pensions by 1 percentage point of gross domestic product and raise a further one per cent or €1.8 billion by increasing value-added tax on products ranging from drugs to electricity, the sources said

Merkel, the EU’s most powerful leader, said the end was not yet in sight in the talks, telling a news conference: “The talks are far from reaching a conclusion.”

She has tried to force the pace this week, at least partly to avoid a Group of Seven summit she will host in Bavaria from Sunday turning into another crisis session on the euro zone, highlighting Europe’s difficulty in solving its own problems.

Her spokesman said Tsipras would not be invited to the G7.

Dijsselbloem said the Brussels talks that ran beyond midnight had narrowed down the remaining issues but differences were “still quite large” and Athens was expected to present alternatives to some of the lenders’ proposals within days. An EU source said Tsipras could return to Brussels for further talks during the night or today, possibly along with top IMF and ECB officials

Time is running out to clinch a deal and get disbursements approved by national parliaments before the bailout programme expires at the end of June.

In one concession, the lenders were offering to unlock 10.9 billion euros in unused bank bailout funds that would enable Greece to cover its financial needs through July and August – more than the €7.2 billion left in the expiring bailout.

As details of the confidential lenders’ proposal trickled out, members of Tsipras’ government and his Syriza party denounced the conditions as unacceptable.

The backlash highlighted the risk of a revolt in Syriza if the Prime Minister decides he has to accept a deal, not least because a big majority of Greeks want to stay in the eurozone.