The one-month implied volatility rose to around 14 percent , its highest since late 2011, with investors buying options that were skewed towards more euro weakness.
Greek Prime Minister Alexis Tsipras shocked European officials by calling for a referendum to be held on July 5 to ask voters to decide whether to accept the bailout terms that his government opposes. Athens also closed banks and imposed capital controls to prevent a collapse of its banks as anxious investors pulled out their cash.
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