Greek party leaders must send euro zone finance ministers the requested written confirmation of commitment to reforms because Greece's creditors need reassurance Athens will stick to reforms after the next elections, the Greek prime minister said.

Lucas Papademos, who heads the Greek national unity government, said euro zone governments and the International Monetary Fund pledged to finance Greece for a long time, much longer than the expected life of his government, and needed commitment from Greece for the corresponding period.

The leader of one of the Greek parties, Antonis Samaras, is refusing to provide such a written commitment, saying his vote in parliament is commitment enough. Without such a letter, the euro zone will not release the next tranche of aid to Greece.

Elections in Greece are tentatively scheduled for February 19th.

"This letter by the leaders of the parties supporting the government, as been requested by the Eurogroup and the IMF...it is necessary in order to eliminate uncertainties and ambiguities concerning actions to be taken in the future, by parties that may be in power," Mr Papademos said.

"But it's up to the leaders of the relevant parties to decide how this confirmation of the commitment will be made."

"I think we should all realise that our European partners and the IMF are committing themselves to the financing of Greece over a long period of time. And this is the reason why they are expecting a corresponding commitment, not only by this government, but also by the political leaders of the parties that support it, on their continued support and commitment to these policies over the medium and long term," he said.

Reuters