NEW YORK (TheStreet) -- Time is running out for Greece as eurozone finance ministers continue a fourth day of negotiations in Brussels ahead of the European Union summit next week.

European leaders have become increasingly frustrated with the Greek government's refusal to accept the latest proposal from creditors that would release $8 billion of bailout funds. Greek Prime Minister Alexis Tsipras is standing firm against the eurozone's demands for deeper spending cuts, higher VAT charges and a reform of the pension system.

German Finance Minister Wolfgang Schaeuble expressed his concern that Greece has "moved backward" in terms of its demands, adding that "the decision lies exclusively with those responsible in Greece."

Greece's Finance Minister Yanis Varoufakis will argue Greece's reformed proposal as negotiations continue.

Critics have argued that the Greek proposal contains too much emphasis on increasing taxes as opposed to cutting spending.

Creditors also wish to cut benefits paid to some low-income pensioners which is a particular point of contention for the Greek Syriza party.

With a $1.8 billion repayment to the International Monetary Fund due on Tuesday, the clock is ticking for Greece. The European Central Bank has made clear that it won't continue to prop up Greek banks if an agreement isn't reached.

If the bailout terms expire without a solution, Greece will default on repayments and may have to exit the eurozone. Even if a deal is struck before the June 30 deadline, Tsipras must then pass the new terms through his parliament, as must other European countries.

Despite the turmoil and uncertainty in Greece, the stock market seemed optimistic that a deal could still be reached, with Greek bonds and stocks both trading higher since the start of the week.

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