Moody's lowered its assessment of the highest rating that can be assigned to a domestic debt issuer in Greece by four points to Caa2 "on the increasing risk of an exit by the country from the euro area," the rating agency said on Saturday.

"Moody's indicated that although the risk of a euro exit by Greece is substantial it is still not what it considers its "central case" or most likely scenario. Following the June 17th Greek parliamentary elections, it is possible that the risk of euro exit will increase further. If that were to occur, the maximum rating Moody's would assign to Greek securities would fall further," the agency said in a statement.

The highest rating of any Greek security is now at B1. France's Societe Generale has said in its report that the possible loss of the Greece's exit might amount to 360 billion euros or 3.8 percent of eurozone's gross domestic product level.

Greece is trying to avoid default and withdrawal from the eurozone by implementing an austerity program in exchange for multi-billion-dollar loans from the EU and International Monetary Fund.

Athens is planning further austerity measures to save some $33 billion through 2015. The country's total debt has ballooned to $490 billion.