Greece continued to adopt a defiant tone toward its creditors, saying it would not make any further compromises even as the country missed a self-imposed Sunday deadline on negotiations. Against this backdrop, fissures began to appear within the ruling Syriza party over Friday's appointment of a lawmaker, who previously supported numerous pro-austerity measures.

The heads of several major institutions involved in negotiations with Athens, including German Chancellor Angela Merkel, European Commission head Jean-Claude Juncker and French President Francois Hollande met for talks on Monday night to come up with a “final proposal” they intend to present to Greece, BBC reported.

Government spokesman Nikos Filis also indicated on Tuesday that Athens would not make any more compromises with its creditors. “If we’re talking about an ultimatum ... which is not within the framework of the popular mandate, it is obvious that the government cannot co-sign and accept it,” Filis told local station Antenna TV, Reuters reported.

Greek Prime Minister Alexis Tsipras also wrote a defiant op-ed published in French daily Le Monde on Sunday, accusing the creditors of making “absurd proposals” that undermined Greek democracy.

EU Economy Commissioner Pierre Moscovici said on Tuesday that Athens had offered pensions reform measures -- a demand previously made by its European creditors, according to Reuters. The Syriza party came to power in January after it promised to defy the pension reform and other austerity measures demanded by its creditors.

An unnamed Greek government official said that the government would be willing to make the IMF payment as agreed upon if it could reach an agreement with creditors. "If we judge that a deal has been sealed, then we will make the June 5 payment normally," the official said, according to Reuters, adding that the money would go through even if there was only a preliminary agreement in place.

Meanwhile, fault lines were exposed in the Greek government on Monday night as the administration’s nominated representative, who was slated to hold talks with the International Monetary Fund (IMF), was forced to resign days after her appointment. Elena Panaritis' appointment was opposed by over 40 Syriza lawmakers, who said her history as a member of the center-left Panhellenic Socialist Movement (Pasok) made her unfit for the far-left Syriza government.

“Her political background is completely at odds with the values, perceptions and policies which Syriza represents. ... This a wrong decision,” the lawmakers said in a letter, according to Financial Times. Panaritis had voted in favor of several austerity measures in 2010 that Syriza has pledged to roll back.

The possibility of an internal revolt in Syriza was raised further when Labor Minister Panos Skourletis warned Tuesday: “When you are elected you are not given carte blanche,” adding that if the debt negotiations fail to reach an amicable solution, “then we’ll have elections,” the Guardian reported, citing Greece's Skai TV.

Greece faces a Friday deadline for a 300 million euro ($330 million) payment to the IMF. It has so far received two bailout packages collectively worth 240 billion euros since 2010, but is locked in negotiations over access to a further 7.2 billion euros in aid. Greece’s battered finances mean that it does not have access to traditional capital markets and must rely on the bailout funds. Several government officials have warned that the country’s coffers are running dangerously low, raising the specter of a possible Greek exit from the eurozone.