A situation where no government is formed may prompt fresh elections, while one that backtracks on austerity agreements may put the country's crucially needed bailout at stake. In either case, analysts say the chance of a Greek exit from the eurozone currency bloc can't be ruled out. 

"Greece is a big concern," said David Jones, chief market strategist at London-based IG Index, adding that such a situation would "definitely inject a lot of volatility into the market." Still, Jones cautioned that it may be awhile until the picture there becomes clearer.

Eurozone blue chips sold off by 2.1%. The euro fell 0.28% to $1.3015. 

On the corporate front, McDonald's (NYSE:MCD) said its global same-store sales climbed 3.3% in April, a slimmer gain than the 4.29% analysts expected, according to Dow Jones Newswires.