Speaking in Berlin on Friday at an unrelated event, Merkel indicated that if negotiators from Greece's left-wing Syriza government failed to come up with a proposal that would satisfy its European Union and International Monetary Fund (IMF) creditors prior to Monday's emergency summit in Brussels, EU leaders would not be able to greenlight a deal.

Merkel said the EU heads of state and government would not be able to sign off on a deal that would prevent Greece from defaulting on its debt at the end of the month, unless a "basis for a decision" was already on the table. In other words, Greece's negotiators would need to convince the EU and IMF with a new package of economic reforms prior to Monday.

Time ticking away

This came as time continued to tick toward a June 30 deadline for Greece to make a 1.6-billion-euro ($1.8 billion) payment to the IMF. It is thought that Athens would most likely default on that payment if it fails to unlock the last 7.2 billion euros of its international bailout.

Before that, the EU and IMF have said they want to see credible proposals from Syriza about how it plans to bring down Greece's massive debt. Greece's previous government had already gone down this path, introducing unpopular austerity measures. However, Syriza swept to power in January after forcing an early general election, winning over voters on an anti-austerity platform.

There were no signs on Friday that the two sides were any closer to a deal than previously, and there were more expressions of frustration with the Greeks from their EU partners.

"We are close to the point where the Greek government will have to choose between accepting what I believe is a good offer of continued support or to head towards default," said European Commission President Jean-Claude Juncker.

Speaking after a meeting of his EU counterparts in Luxembourg, German Finance Minister Wolfgang Schäuble did not appear optimistic.

"I am not really sure that I will be able to share sensational news on Monday," Schäuble said.

Tsipras upbeat

The Greek prime minister, though, expressed optimism that a deal would get done in time to avoid a default and possible "Grexit" scenario, which would see Greece leave the eurozone and possibly even lose its membership in the EU.

Alexis Tsipras insisted that "crisis and terror" would be foiled and that he would reach a deal with the EU and IMF to keep the country afloat.

This came as Greeks continued to plunder their bank accounts, with local media reporting that they had withdrawn around 3 billion euros over the past week alone.

pfd/cmk (AP, Reuters, AFP, dpa)