Greece formally requested on Thursday the International Monetary Fund (IMF) to repay the loan installments due this June with a delay, according to the Central Bank of Greece.

Athens had to repay a 300 million euros (about 336 million U.S. dollars) installment on June 5, the second on June 12, the third on June 16 and the final one for this month on June 19. The total sum amounted to 1.5 billion euros.

With a debt deal with international creditors on the next round of fiscal adjustment and reforms in exchange of further financing still pending after four months of negotiations, Greece struggles to cover its financial obligations.

With state coffers running out of cash and the two sides still holding diverging views in key issues, fears of an imminent credit event and Grexit have increased.

Under IMF's framework in case of failure to repay an installment a country does not face a credit event within hours, but enters a one-month grace period.

The last time a country made such a request to the IMF was four decades ago by Zambia, analysts noted.

"Do not worry," Greek Prime Minister Alexis Tsipras told media in the early hours of Thursday when asked if Greece would pay on Friday after a meeting with European Commission President Jean-Claude Juncker in Brussels.

As negotiations continue, Tsipras announced that he will address the Greek parliament on Friday.