Eurozone finance ministers and Greece’s creditors are to draw up emergency measures on Saturday to cope with a default by the debt-ridden country unless the Greek prime minister, Alexis Tsipras, accepts the creditors’ terms for a five-month extension of Athens’ bailout.

Greece has its last chance to bow to the lenders’ terms following five months of stalemate at a meeting of eurozone finance ministers in Brussels on Saturday afternoon, the fifth such session in 10 days.

Fearing a financial implosion and social unrest in the event of the negotiations collapsing, the ministers are scheduled to draw up plans on Saturday that could involve Greece imposing capital controls, including curbs on ATM withdrawals, to stem a flood of funds out of the ailing Greek financial system.

The creditors have prepared a new funding offer, providing a lifeline to keep Greece afloat until the end of November by extending the bailout by five months and supplying €15.5bn (£11bn) in loans tied to budget cuts and tax rises.

As a two-day EU leaders’ summit ended in Brussels on Friday, several senior officials said Tsipras had to make a choice between accepting the creditors’ ultimatum or embarking on a road that could take Greece out of the euro. The chances of saving Greece were put at 50-50.

Angela Merkel, the German chancellor, who talked privately with the Greek leader in Brussels on Friday morning, urged him to go the “extra step” and accept what she described as “a very generous offer”.

She ruled out any more emergency summits on the Greek crisis and delivered a pointed message to Tsipras by stressing how, during the Cyprus bailout two years ago, Cypriot banks had to be closed “for a few days”, forcing the political leaders to come to Brussels to deal with the creditor institutions and the Eurogroup finance ministers in order to resolve the issue.

The ECB is keeping Greek banks on life support by providing €89bn worth of emergency funding, which is being topped up to keep pace with deposit withdrawals that hit more than €4bn last week alone.

“The European Union founding principles were democracy, solidarity, equality and mutual respect. It was not based on blackmail and ultimatums. No one has the right to put in danger these principles,” he declared.

The Greek labour minister, Panos Skourletis, said: “We have moved from a take-it-or-leave-it scenario to the proposal of a five-month extension that makes no sense.” Tsipras called an emergency cabinet meeting in Athens on Friday evening.

“Nothing is moving, neither side is budging,” said an EU source of thenegotiations going on behind the scenes. “It’s hard to see a deal because no one here believes the Greeks any more. No one trusts them.”

But other sources said there was now little in fiscal and budgetary terms dividing both sides and that the problem was more political than financial.

“The differences are very slight,” said another official.

On the nitty-gritty of fiscal targets, spending plans and cuts, tax increases and economic reforms, both sides were said to be closer than before. On VAT rates and and taxable products, for example, there was only a gap of €107m between the sides. Privatisation and pension reform issues had been essentially settled, while the creditors were still demanding a doubling of defence budget cuts to €400m.

Tsipras has consistently maintained that the dispute is about politics more than money and can only be settled at the highest political levels. This has failed in two EU summits this week. He now faces the political choice of buckling or defying the creditors.

“I am not very optimistic,” said Jean-Claude Juncker, the president of the European commission, who has racked up at least 15 hours of negotiations with Tsipras this week.

The two-page paper on extending the bailout includes a footnote referring to the issue of debt sustainability, allowing the interpretation that the eurozone could eventually accede to a form of debt relief for Greece, which is Tsipras’s primary demand.

But any debt restructuring or rescheduling action would come with strings attached and would be the subject of later tough negotiations. The deal that may or may not be struck on Saturday wouldtherefore buy time for both sides without tackling core issues.

On Friday evening, EU officials said Tsipras had about 20 hours to make up his mind. If he capitulates, he would need to rush budget legislation through the Greek parliament on Sunday to allow the German parliament to endorse the package on Monday before it expires on Tuesday. “Otherwise he won’t get the extension,” said an official.

Teams of financial negotiators are to meet in Brussels on Saturday morning before the finance ministers’ meeting.