An envoy from the International Monetary Fund says European countries must decide how to plug potential funding gaps for Greece next year before the IMF can release the next batch of loans.

The European leaders have tough decisions to make on the issue at a summit late this month..

The next loan payment is an $18 billion installment out of an overall $160 billion rescue package set aside for debt-hit Greece last year by the IMF and the European Union. Athens needs the funds to pay next month's bills.

The Greek debt has exploded to over $500 billion. Most experts agree a planned austerity program needs to be implemented soon for the country to keep up its payments.

European leaders are to meet in late June to discuss Greece's ongoing economic difficulties. An additional multi-billion-dollar rescue package is expected to be debated.