Greece will head to default and a potential exit from the euro zone as well as the European Union (EU) should a deal not be clinched soon with international lenders, Greece's central banker Yannis Stournaras warned Wednesday.

"Failure to reach an agreement would mark the beginning of a painful course that would lead initially to a Greek default and ultimately to the country's exit from the euro area and -- most likely -- from the European Union," according to the central Bank of Greece's annual report on monetary policy.

The report warned about dire consequences to the Greek economy and society in case of failure to break the current impasse in negotiations.

After five months of talks over the details of a reform-for-cash deal, time is running out for Greece amid fears a breakthrough may not be reached.

On June 30, the extension of Greece's second bailout expires and Greece must repay 1.5 billion euros (1.69 billion U.S. dollars) of delayed loan installments to the International Monetary Fund.

Greece's Leftist government has implied that without a deal by then, the payment will not be made.

"We aim to cover our financial obligations on time, but until then several factors might affect liquidity," Deputy Finance Minister Dimitris Mardas told a local TV station Wednesday.

Meanwhile, the outflow of deposits from local lenders was on the rise amid scenarios of looming capital controls in the coming weeks.

According to the Bank of Greece, about 30 billion euros have been withdrawn by Greek banks from October 2014 until May 2015 due to political and financial insecurity.

According to Greek media reports, citing bankers, on Monday Greeks withdrew about 450 million euros and on Tuesday about 700 million euros, as Greek officials exchange harsh statements with European officials on which side is responsible for the deadlock.

Amid this climate, concrete results are not expected from Thursday's Eurogroup meeting and an EU summit next week.

Tensions increased also within Greece.

The main opposition conservative New Democracy spokesman Kostas Karagounis suggested on Wednesday that Prime Minister Alexis Tsipras and his government did not honestly seek a compromise deal with creditors from the start but intentionally wasted time to lead to a rift and Grexit.

Meanwhile, ruling radical Left Syriza MP Costas Lapavitsas urged for a return to the drachma. Syriza's European Parliament member Manolis Glezos called for a moratorium that will freeze all Greece's financial obligations to lenders for a few months to allow more time to strike a viable agreement.