By Jussi Rosendahl and Philip Blenkinsop

HELSINKI/BRUSSELS (Reuters) - The European Union's top economic official sought to rule out any write-off of Greece's debt to governments on Thursday after a European Central Bank policymaker said for the first time that a "haircut" on part of it was probable.

A row between euro zone governments and the International Monetary Fund over how to make Greece's giant debt mountain manageable is holding up the release of 31 billion euros ($39.5 billion) in emergency loans needed to keep Athens afloat.

IMF officials have argued that some write-down for euro zone governments is necessary to make Greece solvent but Germany, the biggest contributor to the bloc's bailout funds, has repeatedly rejected the idea of taking a loss on holdings of Greek debt, saying it would be illegal.

German Chancellor Angela Merkel said after talks with French Prime Minister Jean-Marc Ayrault that they had not discussed a Greek debt write-off and Berlin's position had not changed. They both called for an early solution.

"Of course we did not talk about debt haircuts, you know our view and that has not changed, nor should it," Merkel said.

EU Economic and Monetary Affairs Commissioner Olli Rehn told reporters in Helsinki: "The solution will be a combination of various elements, one is not enough.

"But it is essential that the principal not be touched. There is a strict unanimity on this within the euro zone."

Rehn's comment contradicted ECB Governing Council member Luc Coene, who was quoted by a Belgian daily as saying that a partial write-down of Greek debt was likely to happen eventually.

De Standaard said Coene made the comments in a debate with students at Ghent University on Wednesday. He was also quoted as saying Spain should urgently seek a bailout.

Asked whether the Belgian central bank chief had been reflecting a growing view in the ECB that an official sector "haircut" on Greek debt was inevitable or speaking for himself, a senior ECB source said Coene had expressed his personal view.

Greece's total debt is forecast to rise to 190 percent of gross domestic product next year and seems highly unlikely to fall back to 120 percent of GDP by 2020, the level the IMF has said is the maximum sustainable in the long term.

Banks, insurers and other private investors holding about 206 billion euros of Greek bonds took a savage "haircut" on the nominal value of their securities earlier this year.

HAIRCUT

The euro zone's debt crisis began in Greece three years ago when a newly elected government disclosed that the country had knowingly understated its budget deficit.

Athens managed to sell nearly 1 billion euros in short-term bills on Thursday to complete raising the 5 billion euros it needs to pay off maturing paper on Friday and avoid default.

But the government desperately needs the next tranche of its international bailout loans to recapitalize its banks and pay civil servants and suppliers.

A senior euro zone source told Reuters on Wednesday that finance ministers of the 17-nation currency area would only attempt to close Greece's financing gap to 2014 when they meet again in Brussels next Tuesday, instead of finding a solution up to 2020 as sought by the IMF. [ID:nL5E8MEEF0]

"We will concentrate on 2013 and 2014. The sum is about 13.5 billion euros ($17.2 billion)," said the source involved in negotiations, speaking on condition of anonymity.

That might postpone a longer-term solution to the Greek debt problem until after a September 2013 German general election, but it may not be acceptable to the IMF. Continued...