The International Monetary Fund delegation has left negotiations on Greece's stalled debt talks in Brussels and flown home because of major differences with Athens.

The surprise IMF move on Thursday came as the EU told Greek Prime Minister Alexis Tsipras to stop gambling with his cash-strapped country's future and take the crucial decisions needed to avert a devastating default.

A Greek source told the Reuters news agency that the entire Greek delegation that had been negotiating a cash-for-reform deal had also left for home on Thursday, citing continuing disagreements.

"There are major differences between us in most key areas," IMF spokesman Gerry Rice said in Washington.

"There has been no progress in narrowing these differences recently and thus we are well away from an agreement."

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Greece needs a deal to unlock aid before the end of the month when it is otherwise set to default on a $1.8bn repayment to the Washington-based IMF.

That could trigger capital controls and possibly push Greece out of the eurozone, with unpredictable consequences for financial markets and the European economy.

Rice said the sticking points remained pensions, taxes, and financing. The IMF technical team had returned to the US but remained "fully engaged" with Athens.

European stocks fell after the IMF comments.

Athens stood by its assertions of recent days that all is not lost.

"The Greek delegation, as agreed, is ready to intensify deliberations in order to conclude a deal soon, even in the coming days," spokesman Gabriel Sakellaridis said.