Crucial negotiations between the Greek government and its private creditors on a bond swap deal needed to avoid default have appeared close to collapse.
Representatives of private bondholders said they had been "paused for reflection".
The bond swap aims to reduce Greece's debt by 100 billion euro (£84 billion) and is a key part of a second, 130 billion euro (£109 billion) international bailout.
Without it, the country could suffer a catastrophic bankruptcy that would send shockwaves through the global economy.
The bailout tops a first, 110 billion euro (£92 billion) programme agreed in May 2010, when the country borrowing costs soared to untenable heights.
Prime Minister Lucas Papademos and Finance Minister Evangelos Venizelos met on Thursday and Friday with Charles Dallara and Jean Lemierre of the Institute of International Finance (IIF), a global banking body representing private bondholders to discuss the deal.
"Unfortunately, despite the efforts of Greece's leadership, the proposal put forward ... which involves an unprecedented 50% nominal reduction of Greece's sovereign bonds in private investors' hands and up to 100 billion euro of debt forgiveness - has not produced a constructive consolidated response by all parties, consistent with a voluntary exchange of Greek sovereign debt," the IIF said in a statement.
"Under the circumstances, discussions with Greece and the official sector are paused for reflection on the benefits of a voluntary approach," it said. "We very much hope, however, that Greece, with the support of the Euro Area, will be in a position to re-engage constructively with the private sector with a view to finalising a mutually acceptable agreement."
Earlier, a senior Greek government official said the talks would likely resume next week.