U.S. President Barack Obama held talks on the telephone with Greece's Prime Minister Alexis Tsipras late on Tuesday, during which Obama expressed Washington's "strong desire for a successful outcome" in the negotiations. 

Alexandros Lamnidis, general manager of the Greek Tourism Confederation (SETE), told CNBC on Tuesday that SETE wants Greece to remain a member of the currency union.

The bank holiday imposed by the government has forced some tourism professionals in northern Greece and on the Aegean islands to start accepting transactions with Bulgarians, Turks and other international holidaymakers in their own national currencies.

The eurozone has given Greece until Thursday to present new proposals to secure a deal with creditors, and has called a full EU summit for Sunday.