U.S. stocks fluctuated in midday trading today, after the Standard & Poor’s 500 Index produced its biggest two-day gain since April, as investors watched geopolitical developments and energy shares sank after Brent crude reached a nine-month low.

Nuance Communications Inc. tumbled 11 percent after posting third-quarter revenue that missed analysts’ estimates. Chevron Corp. slipped 1 percent to lead losses among large stocks. Intercept Pharmaceuticals Inc. soared 24 percent after a clinical trial met its primary goal.

The S&P 500 fell 0.1 percent to 1,935.44 at 12:44 p.m., trimming an earlier decline of 0.4 percent. The Dow Jones industrial average slipped 1.89 points, or less than 0.1 percent, to 16,568.09. Trading in S&P 500 stocks was 26 percent below the 30-day average at this time of day.

“We’re in a zone of ambivalence with investors maintaining a cautious bias,” Terry Sandven, chief equity strategist at Minneapolis-based U.S. Bank Wealth Management, which oversees $124 billion, said by phone. “Equities appear to be navigating the dog days of summer with markets being driven more by geopolitical events than economic and company fundamentals.”

The S&P 500 climbed 1.4 percent in the past two trading days amid speculation that tension in Ukraine would lessen. The S&P 500 had fallen 3.9 percent from its record of 1,987.98 on July 24 on concern that conflicts from Iraq to Israel and Ukraine could slow global economic growth.

Humanitarian Mission

Data today from Germany reignited those concerns, after investor confidence reported by the ZEW Center dropped for an eighth month as the crisis in Ukraine and a sluggish euro-area recovery damped the outlook for Europe’s largest economy.

A Russian humanitarian mission was headed toward eastern Ukraine after the U.S. warned President Vladimir Putin not to use aid as a cover to send in troops. Ukraine said it won’t let the convoy enter in its current form because it argues the mission doesn’t adhere to international rules.

Equities pared declines after Russia’s Foreign Minister Sergei Lavrov called on Germany to assist with the aid mission. Lavrov spoke by phone with German Foreign Minister Frank-Walter Steinmeier today, the Russian Foreign Ministry website said.

In the Middle East, wide gaps remain between Israel and the Palestinians in reaching a long-term deal on the Gaza Strip, an Israeli official said, as Hamas warned there would be no more truces beyond the one due to end at midnight tomorrow.

Iraq’s Prime Minister Nouri al-Maliki chaired a meeting of military officers in the latest sign that he won’t hand power to designated successor Haidar al-Abadi.

“We have some bad news on German investor confidence, and bad news from the euro zone in the long term impact the U.S.,” Walter Todd, who oversees more than $1 billion as chief investment officer for Greenwood, South Carolina-based Greenwood Capital Associates LLC, said in a phone interview. “The economic data from the U.S. is very good, but if the economic situation in Europe continues to deteriorate, we’re not going be immune from that forever.”

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