US markets turn negative

The US markets turned negative as investors continue to cautious about Greece's ability to meet its debt obligations.

The Dow Jones Industrial Average was down 143.57 points, or 1.35%, at 10,511.73. The Standard & Poor's 500 Index was down 9 points, or 0.83%, at 1,090.16. The Nasdaq Composite Index was up 0.72 points, or 0.03%, at 2,335.11.

In earlier trading session, the overall stock market trimmed losses on comments from Federal Reserve Chairman Ben Bernanke that he was ready to take more steps to help the fragile recovery.