Tsipras blames creditors for stalled talks

"It is due to the insistence of certain institutional actors on submitting absurd proposals and displaying a total indifference to the recent democratic choice of the Greek people”.

He said Greece is the victim of "a conflict between two diametrically opposing strategies concerning the future of European unification".

While "the first strategy aims to deepen European unification in the context of equality and solidarity between its people and citizens", he noted, the other seeks "the split and the division of the eurozone, and consequently of the EU".

He warned that "Europe is at a crossroads”, but said his government cannot do any more to meet demands.

"Following the serious concessions made by the Greek government, the decision is now … in the hands of Europe’s leaders”.

Pension and labour market reforms remain the sticking points in the negotiations

But Tsipras said the Greek pension system has been weakened by "the extreme austerity programme that has been implemented in Greece since 2010". He said demands on labour would "flagrantly violate European labour legislation".

A few hours after his op-ed was published, Tsipras held a phone-conference with Germany's Angela Merkel and France's Francois Hollande.

It was their second call in three days, in a sign that any deal depends on agreement at the highest level.

There’s also a chance the three leaders will meet in Berlin on Monday.

Merkel, Hollande and European Commission president Jean-Claude Juncker will be in the German capital for a business summit and Tispras, according to unconfirmed reports, could join them in the margins.

IMF deadline

The strident rhetoric comes as the clock tics toward another repayment deadline.

Greece is meant to pay €300 million back to the International Monetary Fund (IMF) on Friday (5 June).

Some EU leaders are beginning to say a Greek default could be contained by the eurozone “firewalls” imposed after the financial crisis.

For his part, Juncker, speaking in an interview with the Sueddeutsche Zeitung, warned that a Greek exit fan "the idea that the euro is not irreversible".

"I don’t share this idea that we would have less worries and constraints if Greece abandoned the euro," he said.

But he also said he "cannot imagine" the EU would continue to help Greece without the IMF.

Christine Lagarde, the IMF chief, has hinted that it might not participate in any top-up Greek rescues. But Juncker noted that “without the IMF, it won’t work”.

The Greek economy minister George Stathakis on Sunday said his country would meet its IMF commitment.

“The country has been servicing its loans through internal resources for the past year. It will do the same this time”, he told Greece's Real News daily.

Deadlines multiply

But even if Greece finds the money by Friday, it needs to find still more to pay pensions and salaries, as well as another €900 million for the IMF later in June.

"Greece has not been paying its bills for weeks," EU commissioner Guenther Oettinger told Germany’s Die Welt on Monday.

He added that Greece could opt to repay the IMF in one instalment at the end of the month instead, gaining more time to try to unblock the last €7.2 billion tranche of its bailout before the later deadline.

"It's up to the Greek government to decide whether to propose to bundle its IMF payments in June and win some days' time", he said.