The Dow Jones industrial average lost 98 points, or 0.78%, to 12,528. The S&P 500 Index dropped 8 points, or 0.66%, to 1,323. The Nasdaq Composite fell 21 points, or 0.76%, to 2,853.
Investors showed little reaction to US data that showed initial jobless claims fell by 6K to 386K last week, while Q1 GDP revision came in line with expectations at 1.9%.
European stocks were broadly lower, with the Stoxx Europe 600 index down 0.9%, as the summit gets underway. Gold lost 1.0% to $1562 an ounce, while crude-oil futures dropped 0.7% to $79.62 a barrel.