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Geert Vanden Wijngaert, Associated Press
Dutch Finance Minister Jeroen Dijsselbloem, center, speaks with German Finance Minister Wolfgang Schaeuble, left, and Irish Finance Minister Michael Noonan, right, during a roundtable meeting of the eurogroup finance ministers at the EU Council building in Brussels on Monday, May 11, 2015. Hopes for a deal between Greece and its European creditors at a key meeting Monday are slim, weighing on the region's stock markets as the country struggles to make upcoming debt repayments.

BRUSSELS — Greece has made progress in talks with creditors but "more time and effort" is needed to reach a deal to give the cash-strapped country vital rescue money, the eurozone's top official said Monday.

Jeroen Dijsselbloem said after a meeting of the eurozone's 19 finance ministers that negotiations have "advanced" and that "important progress" is being made.

However, he said "more time is needed to bridge remaining gaps" to reach a comprehensive agreement on the reforms Greece must make in exchange for more loans.

He also warned that if Greece wanted to hold a referendum on any eventual deal, that may hold up payment of the funds, which the creditors will only hand over when the reforms are being implemented.

"There are time constraints and liquidity constraints and hopefully we will reach an agreement before time runs out and before money runs out," said Dijsselbloem.

Greece is facing a cash crunch that could see it go bankrupt within weeks and possibly leave the euro currency. It has for over three months been trying to agree on a list of reforms and budget measures to get a bailout loan — worth 7.2 billion euro ($8 billion) — that will help it pay upcoming debts.

Earlier Monday, Greece said it had given the go-ahead to make a big debt repayment worth 757 million euros ($844 million) to the International Monetary Fund due Tuesday. But it will have trouble meeting other repayments in the following weeks.

Greek finance chief Yanis Varoufakis said "there has been considerable convergence" in the talks over recent weeks but that it was primarily because of concessions made by his government.

He conceded his disappointment that there has yet to be a firm agreement on giving Greece the rescue loans but that discussions are taking place "in good spirits."

In the event of a debt default, Greece could have to put controls on the flow of money through its banks and eventually even drop out of the euro altogether. Despite three months of talks, Greece and its creditors have failed to agree on further reforms and savings Athens needs to qualify for the loan installment.

Greece hasn't had any bailout money since last August and has relied on its own resources.

Whether Greece will default on its debts and leave the euro is one of the biggest uncertainties surrounding the global economy. Most stock markets in Europe were trading lower Monday, with Athens' main index down 2.5 percent.

Greece's left-led government was elected in January on a mandate to end crippling austerity policies, blaming them for the parlous state of the economy. The budget cuts required in return for 240 billion euros worth of rescue loans contributed to a massive shrinkage in the Greek economy and the sky-rocketing of unemployment and poverty.

The Greek government has indicated it will reject any deal that doesn't guarantee a credible prospect of ending its economic crisis. It has hinted at a possible referendum on any deal that runs counter to its electoral mandate.

German Finance Minister Wolfgang Schaeuble said it "could be perhaps a correct step to let the Greek people decide."

Back in 2011, Greece's then prime minister, George Papandreou, floated the idea of a referendum on Greece's bailout but was rebuked by his counterparts in Europe.

"The decision lies with Greece," Schaeuble said. "We just want to help Greece, but Greece must do its part as well."

Dijsselbloem said it's every country's right to call a referendum but warned that the disbursement of bailout funds may not be made if implementation of the reforms hasn't started.