Stock index futures fell on Thursday along with European shares as concerns resurfaced about the euro zone banking system.

Futures had been solidly positive early following a sharp drop for indexes in the previous session. The swing suggested more volatility ahead. The Dow has fluctuated in a range of more than 400 points for five straight days.

The S&P slumped 4 percent on Wednesday, while the Dow lost 4.6 percent.

European shares were pressured early Thursday as French banks fell, extending the previous day's losses on concerns about the sector's outlook. Reuters reported that one bank in Asia had cut credit lines to major French lenders.

As Europe pares back, that's going to have an impact on us, said Robert Pavlik, chief market strategist at Banyan Partners LLC in New York. There's still a lot of concern about Europe and French banks, suggesting there's still a lot of volatility left in this market.

U.S. stocks had some bright spots. Dow component Cisco Systems Inc advanced 12 percent to $15.37 in premarket trading a day after reporting quarterly revenue and profits that topped scaled-back expectations.

News Corp rose 3.6 percent to $14.20 before the bell after it posted higher operating profit and revenues.

When we're eventually able to return our focus to fundamentals, the good news out of Cisco and News Corp will help, Pavlik said.

S&P 500 futures fell 17.8 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 sank 118 points, and Nasdaq 100 futures lost 24.25 points.

Corporate earnings this season have generally been strong, with a majority of companies topping Wall Street expectations for both profits and revenues, but the results have been overshadowed by concerns about huge government debt loads on both sides of the Atlantic and the U.S. economic slowdown.

Investors awaited weekly jobless claims data, which are seen remaining unchanged at 400,000. June international trade deficit is expected to narrow to $48 billion from $50.23 billion. Both reports are due at 8:30 a.m. EDT.

Worries about French lenders triggered a selloff in European and U.S. banks on Wednesday and contributed to the sharp decline in broader equities.

(Editing by Jeffrey Benkoe)