Investors in Greece have been rattled by the failure over the weekend to break a months-long deadlock in the country's bailout talks with creditors. Shares on the Athens Stock Exchange were 6 percent lower in early trading, and markets opened lower across Europe.

The talks in Brussels between negotiators from Greece and bailout lenders failed to bridge differences despite mounting pressure on Athens, which has taken the emergency measure of bundling its June repayments to the International Monetary Fund until the end of the month.

Prime Minister Alexis Tsipras on Monday told the Efimerida Ton Syntakton newspaper that eurozone and IMF lenders had demanded a new round of pension cuts, which his government had rejected.