Greek Prime Minister Alexis Tsipras has said he will demand a eurozone summit if creditor talks on Friday fail to break months of deadlock over the country's debt and reform goals.
The impasse has held up the latest instalment of Greece's 86-billion-euro ($92 billion) bailout, agreed in 2015, which it needs for debt repayments in July.
"If the Eurogroup is not in a position to (produce a result) on Friday, I have asked EU President Donald Tusk to call a summit of eurozone countries," Tsipras said after meeting with Tusk in Athens on Wednesday.
Both Tsipras and Tusk insisted, however, that such a step would not be necessary.
Tusk said he had "no doubt" there would be a breakthrough on Friday at the Eurogroup -- the finance ministers of the 19 countries that use the single currency.
"Yesterday we made significant progress and as you know, talks will continue today. I hope that you will be able to find an agreement on Friday in the Eurogroup," Tusk said.
Eurogroup chief Jeroen Dijsselbloem said he was still trying to hammer out a deal.
"Had talks and contacts on Greece during the day. Work continues," Dijsselbloem, the Dutch finance minister, said on Twitter, without elaborating.
EU sources close to the negotiations said they were still some way from the stage where eurozone ministers would hold a teleconference -- usually a sign that a deal is imminent.
"Talks will continue in different formats," they said.
Negotiations between Athens and its eurozone and IMF creditors have dragged on for months amid disagreements on debt relief and budget targets for the country.
The last such impasse over Greece, which followed the election of leftist Tsipras in early 2015, nearly saw Athens expelled from the euro.
- 'Absurd demands' -
Tsipras on Wednesday accused hard-line creditors of making "absurd demands" and "shifting the goalposts".
"(New) demands and requirements arise constantly... the games must stop," he said.
Greek Finance Minister Euclid Tsakalotos on Tuesday flew to Brussels to relaunch the talks, which had once again stalled after bailout monitors left Athens without an agreement.
But Tusk said Wednesday that a deal "will be possible thanks to the readiness of Greek people to sacrifice something."
Athens says its economy is performing better than expected, so it should not be asked to make sacrifices beyond those agreed to as part of its current multibillion-euro bailout -- its third since 2010 -- which ends in 2018.
According to reports, the creditors are refusing to conclude the current audit without a pledge for fresh cuts in 2019.
Among the measures reportedly demanded by the creditors are additional pension cuts, a reduced tax-exemption ceiling, and further deregulation of the energy and labour markets.
But Greece's creditors are themselves also at odds.
The IMF has repeatedly said that Greece's debt is not sustainable and must be restructured, otherwise it will not participate in the bailout.
European governments, especially Germany, have resisted providing more debt relief and dispute the fund's analysis, instead calling for more economic policy steps including pension reforms, tax increases and further privatisations of state-owned enterprises.
With the European Union already reeling from Brexit, Tsipras argued that Greece's current rescue programme would collapse if his government were to fall.
His leftist-led coalition has just 153 MPs in the 300-seat parliament, which would make it difficult for Tsipras to push through another package of unpopular austerity measures.