Publication of the draft Debt Sustainability Analysis laid bare a dispute between Brussels and the Washington-based global lender that has been simmering behind closed doors for months.

Greek Prime Minister Alexis Tsipras cited the report in a televised appeal to voters on Friday to say 'No' to the proposed austerity terms, which have anyway expired since talks broke down and Athens defaulted on an IMF loan this week.

It was not clear whether an arcane IMF document would influence a cliffhanger poll in which Greece's future in the euro zone is at stake with banks closed, cash withdrawals rationed and commerce seizing up.

"Yesterday an event of major political importance happened," Tsipras said. "The IMF published a report on Greece's economy which is a great vindication for the Greek government as it confirms the obvious - that Greek debt is not sustainable."

At a meeting on the International Monetary Fund's board on Wednesday, European members questioned the timing of the report which IMF management proposed at short notice releasing three days before Sunday's crucial referendum that may determine the country's future in the euro zone, the sources said.

There was no vote but the Europeans were heavily outnumbered and the United States, the strongest voice in the IMF, was in favor of publication, the sources said.

The Europeans were also concerned that the report could distract attention from a view they share with the IMF that the Tsipras government, in the five months since it was elected, has wrecked a fragile economy that was just starting to recover.

"It wasn't an easy decision," an IMF source involved in the debate over publication said. "We are not living in an ivory tower here. But the EU has to understand that not everything can be decided based on their own imperatives."

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Greek Finance Minister Yanis Varoufakis said in a blog post the IMF had upheld the Syriza party government's contention for the last five months that debt relief should be at the center of the negotiations.

"Puzzlingly, all this fine research by the good people at the IMF suddenly evaporates when IMF functionaries coalesce with their ECB and the European Commission colleagues in order to impose upon our government their chosen policies," he wrote.

The IMF argues that Greece's debt burden of nearly 185 percent of gross domestic product can only be made sustainable if the euro zone provides considerable extra financing through a mixture of new loans and a debt restructuring.

This is politically anathema in Germany, the biggest creditor country, and most other euro zone states, where no leader wants to explain to taxpayers that the money they lent to Athens will never be coming back.

Euro zone governments insisted in five months of talks this year that a lengthening of loan maturities and a reduction in interest rates would only be considered after Greece had implemented its commitments under a 2012 bailout deal, including painful structural reforms and public spending cuts.