Prime Minister Lucas Papademos told his cabinet on Thursday that international lenders had reacted positively to a letter from Greece's conservative leader that is required to unblock financial aid, according to a minister who attended the meeting.

The European Union and International Monetary Fund have said leaders of all parties serving in Papademos's national unity government must provide a written pledge that they will back austerity measures in return for the loans.

Antonis Samaras, leader of the conservative New Democracy party, had balked at the demand, thereby holding up the release of the next tranche worth 8 billion euros (6.9 billion pounds), before finally sending his letter on Wednesday.

Papademos said the content of the letter was satisfactory. There is an initial positive response to it (from abroad), the minister told reporters, on condition of anonymity.

In his letter, Samaras said he supported Papademos's government and Greece's second international bailout worth 130 billion euros, though he also repeated his call for changing some economic policies demanded as a condition of the bailout.

Samaras, a Harvard-educated economist, wants to change the policy mix to allow Greece's economy to start growing again after four years of recession exacerbated by tax hikes, spending cuts and reductions in wages and pensions.

Without the 8 billion euro tranche -- the sixth instalment of a 2010 bailout worth a total 110 billion euros -- Greece will run out of money next month, defaulting on its debts and raising the prospect of a messy exit from the euro zone.

EU leaders have insisted on the written pledge that Greece's political leaders will continue backing the bailout plan beyond the life of Papademos's interim government because they fear the parties will otherwise try to wriggle out of their commitments.

An election has been pencilled in for February 19. Opinion polls suggest Samaras's party will win most votes but not enough for an overall parliamentary majority.

(Reporting by Renee Maltezou, writing by Gareth Jones)