The International Monetary Fund dramatically walked out of the Greek creditor negotiations and the president of the European Council has issued a stark warning to Athens that “there is no more time for gambling”.

Greece needs its EU and IMF creditors to release bailout funds in order to repay €1.6bn in liabilities due by the end of the month. But both sides have still to reach agreement in a cash-for-reforms deal, pushing the country closer to a potentially disastrous technical default.

“There are major differences between us in most key areas,” said the IMF’s spokesman, Gerry Rice, as the fund’s lead negotiators returned from Brussels to Washington. “There has been no progress in narrowing these differences recently and thus we are well away from an agreement.”

Donald Tusk the European Council president, who had a private meeting with the Greek Prime Minister Alexis Tsipras on 11 June, also issued what amounted to an ultimatum. “We need decisions, not negotiations, now,” he said. “It’s my opinion that the Greek Government has to be, I think, a little more realistic. There’s no more space for gambling, there’s no more time for gambling. The day is coming, I’m afraid, where someone says the game is over”.

Jens Weidmann, the president of Germany’s Bundesbank, added to the pressure, saying that Greece’s “time was running out” to secure an agreement and that “the risk of insolvency is increasing by the day”.

In pictures: Solidarity protest for Greece in London Show all 7 1 /7 In pictures: Solidarity protest for Greece in London In pictures: Solidarity protest for Greece in London London Campaigners hold a solidarity protest for Greece in Trafalgar Square In pictures: Solidarity protest for Greece in London London Campaigners hold a solidarity protest for Greece in Trafalgar Square In pictures: Solidarity protest for Greece in London London Campaigners hold a solidarity protest for Greece in Trafalgar Square In pictures: Solidarity protest for Greece in London London Campaigners hold a solidarity protest for Greece in Trafalgar Square In pictures: Solidarity protest for Greece in London London Supporters blow horns, chant slogans and hold various signs to show support for Greece's new anti-austerity government In pictures: Solidarity protest for Greece in London London Christos Giovanopoulos from the Greek group 'Solidarity For All' speaks against the 'regime of austerity and social barbarism' and how Greece has a chance to escape a country in crisis, now under Alexis Tsipras and the Syriza party In pictures: Solidarity protest for Greece in London London A sign reads 'Merkel Crete is here' as the Greece Solidarity Campaign, Syriza London and other organisations gathered for a mass rally in support of the people of Greece in Trafalgar Square

If Greece fails to make its €1.6bn payment to the IMF by the end of the month, it will be in technical default – which could mean the European Central Bank will no longer accept the country’s bonds as security for emergency liquidity lending. That could prompt the collapse of the Greek banking system.

Mr Tsipras has been in meetings with the head of the European Commission, Jean-Claude Juncker, who has been leading attempts to broker a deal between Athens and its creditors. Despite the departure of the IMF team from Brussels, Mr Rice said “the IMF never leaves the table. We remain engaged – but the ball very much is in Greece’s court right now.”

Gabriel Sakellaridis, a spokesman for the Greek Government, suggested that a deal was coming: “The Greek delegation, as agreed, is ready to intensify deliberations in order to conclude a deal soon, even in the coming days.”