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Updates with analyst comment

By Shashwat Chauhan and Pranav Kashyap

May 15 (Reuters) - U.S. stock index futures slipped on Thursday as euphoria from the U.S.-China tariff truce tapered off, while UnitedHealth was pressured after a report of a DoJ investigation into the health insurer.

Markets are also keenly awaiting commentary from Federal Reserve Chair Jerome Powell, who is scheduled to speak later in the day.

Meanwhile, retail behemoth Walmart's WMT.N shares rose 1.5% in premarket trading after it beat estimates for first-quarter U.S. comparable sales.

UnitedHealth Group UNH.N dropped 5.9% after the Wall Street Journal reported that the U.S. Department of Justice was conducting a criminal investigation into the health insurer for possible Medicare fraud. The company said it had not been informed of a criminal probe by federal prosecutors.

At 07:02 a.m. ET, Dow E-minis YMcv1 were down 130 points, or 0.31%, S&P 500 E-minis EScv1 were down 26 points, or 0.44%, and Nasdaq 100 E-minis NQcv1 were down 125 points, or 0.58%.

Powell's upcoming remarks will be dissected, particularly as several Fed officials suggested earlier this week that policymakers might hold interest rates steady as the U.S. central bank gauges how tariffs and ongoing trade negotiations could ripple through prices and the broader economy.

A spate of economic data, including April's producer prices and retail sales figures as well as weekly jobless claim numbers is due at 8:30 a.m. ET.

The data dump will follow a relatively tame consumer price reading earlier this week, indicating that consumer prices saw a moderate rebound last month.

"Today's PPI, initial claims data and a Powell speech are compelling reasons for risk to take a breather here," said Chris Beauchamp, chief market analyst at IG Group.

In results-driven moves, Cisco Systems CSCO.O gained 3.4% after the networking-equipment maker raised its annual forecasts and named Mark Patterson its new CFO.

It has been a roller-coaster ride for stocks this week as equities surged on Monday and Tuesday after the United States and China agreed upon a 90-day pause on their heated tariff dispute.

These initial advances pushed the S&P .SPX into positive territory for the year, a first since late February, although the index still hovers about 4% below its all-time highs.

However, the rally hit a roadblock in the last session as markets searched for fresh catalysts. The S&P 500 eked out marginal gains, while the Dow .DJI finished in the red.

Many megacap and growth stocks, which had enjoyed strong gains earlier in the week, pulled back, with Nvidia's NVDA.O shares falling 1.3% and Tesla TSLA.O shedding 2.4%.

Other major movers included Foot Locker FL.N, which soared 82.4% after rival Dick's Sporting Goods DKS.N agreed to buy the footwear retailer for $2.4 billion.

Top oil producers Chevron CVX.N and Exxon Mobil XOM.N dropped more than 1% each as oil prices slid more than 3% on expectations of a U.S.-Iran nuclear deal that could result in sanctions easing.

President Donald Trump, who is on a four-day tour of the Gulf region, said the U.S. was getting very close to securing a nuclear deal with Iran and that Tehran had "sort of" agreed to the terms.

(Reporting by Shashwat Chauhan and Pranav Kashyap in Bengaluru, Additional reporting by Rashika Singh; Editing by Saumyadeb Chakrabarty and Pooja Desai)

((Shashwat.Chauhan@thomsonreuters.com;))