High-ranking members of Greece's governing radical left Syriza party say they cannot accept a deal proposed by the country's creditors during a meeting between Prime Minister Alexis Tsipras and the head of the European Union's executive arm.

Tsipras' meeting with Commission President Jean Claude Juncker, which ran into the early hours of Thursday, failed to yield a breakthrough in Greece's protracted negotiations over the release of remaining bailout funds.

Speaking in Brussels after the meeting, Tsipras dismissed some of the proposals by the institutions overseeing Greece's bailout — the European Central Bank, European Commission and International Monetary Fund.

Syriza party secretary Tassos Koronakis said the proposals "cannot form the basis of an agreement."

The Athens stock exchange fell sharply, trading 2.6 percent lower by midmorning.

Discussions are set to continue.