Greece’s foreign creditors insisted on Tuesday that a sixth tranche of rescue funding which the country is relying on to pay its bills through December would not be disbursed unless all the leaders in a three-party interim government provide written guarantees committing to the terms of the latest EU bailout for Greece - a clear nudge to the leader of the conservative New Democracy, Antonis Samaras, who has refused to give his signature.

The stance of Samaras - dismissed by some as posturing - was reportedly the subject of a teleconference on Tuesday between officials of the European Commission, the European Central Bank and the International Monetary Fund, known collectively as the troika.

Sources said that the troika - who are due back in Athens later this week - would not compromise their demands and planned to exert more pressure on the ND leader.

The spokesman for European Economic and Monetary Affairs Commissioner Olli Rehn, Amadeu Altafaj, repeated that Brussels would not take no for an answer. “The Eurogroup as a whole expects Greek political forces to provide a clear and unequivocal commitment to the agreement and we expect this in writing. It has to be a letter and signed,” Altafaj said. “We are not saying exactly how this has to be written down,” he said.

Despite the renewed pressure, sources in Samaras’s office told Kathimerini that the ND leader’s commitments to date were sufficient and that “additional demands go beyond any political logic and morals.”

The sixth tranche of rescue funding, valued at 8 billion euros, is expected to be the focus of talks on Monday in Brussels between Prime Minister Lucas Papademos and European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso.

In a speech in Parliament on Monday, triggering a debate ahead of today confidence vote in the new interim government, Papademos said that the form of the reassurances demanded by Brussels would be “examined.”

In a related development, former Prime Minister George Papandreou said that he felt that, now, without the shackles of his role as premier he would be “freer to intervene” in politics. Meanwhile speculation is mounting about a possible contest for PASOK’s leadership.