U.S. stocks ended July with a more than 300-point selloff for the Dow Jones Industrial Average, a swoon that snapped a five-month winning streak for the broader market.

Traders said there was no single catalyst for the stumble, though selling started early and accelerated into Thursday's closing bell, dragging the Dow into negative territory, down 0.1%, for 2014.

Investors said an upbeat reading from the labor market sowed concerns about the Federal Reserve possibly raising rates quicker than many investors anticipate. Some pointed to disappointing earnings reports from U.S. companies Thursday, which disrupted what has been a strong season for corporate profits. Others pointed to Argentina's default on some bonds and fresh worries that the euro zone's central bank will need to provide more stimulus.

The Dow Jones Industrial Average fell 317.06 points, or 1.9%, to 16563.30. The S&P 500 shed 39.40 points, or 2%, to 1930.67 and the Nasdaq Composite Index dropped 93.13 points, or 2.1%, to 4369.77.

"There are so many things that are coming to a head simultaneously," said Joe Spinelli, head of Americas single stock trading at Deutsche Bank . "Clients are wanting to get into a position to ride out any storm that might pop up."