The German and French leaders Tuesday joined growing calls for debt-wracked Greece to quickly reach a deal with its creditors and avoid default, as crisis talks continued "day and night".
"We must accelerate it because the deadline is approaching," said French President Francois Hollande during a Berlin visit, as Athens suffers a cash shortage and faces hefty loan repayments in the next few months.
German Chancellor Angela Merkel agreed that "the talks should be accelerated" and called for "significant progress" in Athens's negotiations on its bailout programme with the International Monetary Fund (IMF), European Commission and European Central Bank.
The radical anti-austerity government of Prime Minister Alexis Tsipras has been in a standoff with its lenders for four months while battling recession and a liquidity crunch, renewing fears the country could crash out of the eurozone.
The EU and IMF are demanding tough labour market and pension reforms from Greece in return for the final 7.2 billion euros ($8.0 billion) in bailout funds Athens desperately needs.
However the reforms contradict the election promises that swept Tsipras's radical-left party into power in January.
In Brussels talks are "progressing, but at a slow pace" and teams "continue to work day and night," said Margaritis Schinas, spokesman of the European Commission.
"We are making progress, even if I remain cautious," said Eurogroup head Jeroen Dijsselbloem about the talks between Athens and the three institutions.
European Commission president Jean-Claude Juncker said he was confident a deal could be reached "toward the end of May, start of June," speaking with Bloomberg News.
Greek Finance Minister Yanis Varoufakis had said Monday his government was "very close to an agreement" with creditors, which may occur "maybe in a week."
- Time 'very limited' -
Juncker ruled out an aid deal being struck at a meeting of EU leaders on Thursday and Friday in the Latvian capital, telling Bloomberg that "Riga isn't made for that".
Merkel said Tspiras would be among European leaders in Riga and that "we'll see if opportunities for discussion emerge".
Hollande also said "we will have the opportunity to talk to Mr Tspiras" in Riga, without specifying who would join the talks.
He stressed that "we want Greece to remain in the eurozone and to find a lasting solution".
The French and German leaders were the latest to voice concerns about the pace of negotiations, after Europe's Economic Affairs Commissioner Pierre Moscovici said Monday that time was now "very limited".
"They are more eager to say what they don't want to stay in the (bailout) programme than to propose alternatives," Moscovici told a Berlin news conference, while insisting that "some progress" had been made in recent days.
Meanwhile, public doubts about the government's course appeared to be growing in Greece, according to a poll released Tuesday by the University of Macedonia for Skai television.
It showed that for the first time since February, a majority of respondents, 41 percent, disagreed with the government's strategy in negotiations, while 35 percent had a positive view.
Athens' troubles have raised renewed fears of a "Grexit", a scenario that would be "really serious" for Europe, Nobel laureate US economist Joseph Stiglitz warned.
"You really are bringing more instability into Europe," he said in comments to Bloomberg, adding that it could send the euro currency project "down the tubes".