The heads of both the International Monetary Fund and the European Central Bank have attended talks in Berlin in an attempt to reach a deal with Athens.
They joined German Chancellor Angela Merkel, French President Francois Hollande and European Commission head Jean-Claude Juncker at the meeting.
The aim was to come up with "a final proposal" to present to Athens, according to reports.
A €300m (£215m) payment to the IMF is due on Friday.
There are fears Greece does not have the necessary funds to pay and could default on the debt, ultimately leading to its exit from the eurozone.
The country remains at a deadlock with international creditors over the release of €7.2bn in remaining bailout funds.
The fact that International Monetary Fund chief Christine Lagarde and ECB president Mario Draghi both attended the Berlin meeting underlines the seriousness of the talks.
The IMF, ECB and the European Commission all want further austerity reforms in return for the cash, which the Greek government - led by Prime Minister Alexis Tsipras - is refusing.
In a column published by French newspaper Le Monde on Sunday, Mr Tsipras said his government was not to blame for the impasse.
"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 wrote.
Mr Tsipras was not contacted during the emergency meeting, according to reports.
After the meeting, a spokesperson for Ms Merkel told the AFP news agency only that the quintet agreed to work together "intensely" in the coming days and would stay in "close contact".