Stock index briefly added to losses on Thursday after government data showed an unexpected rise in the number of U.S. workers filing new claims for unemployment insurance last week.

Initial filings for unemployment benefits rose 18,000 to a seasonally adjusted 460,000, Labor Department data showed, above the forecast of 435,000.

S&P 500 futures fell 4.9 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 47 points, and Nasdaq 100 futures dropped 7.25 points.

(Reporting by Chuck Mikolajczak)