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US stocks slide lower as investors weigh heightened geopolitical concerns

iStock/Thinkstock(NEW YORK) -- U.S. stocks closed lower Tuesday amid heightened geopolitical concerns.

The Dow Jones Industrial Average slid 6.72 (-0.03 percent) to finish at 20,651.30.

The Nasdaq gave up 14.15 (-0.24 percent) to close at 5,866.77, while the S&P 500 finished at 2,353.78, down 3.38 (-0.14 percent) from its open.

Crude oil prices were under 0.5 percent higher; about $53 a barrel.

Investors are remaining cautious as the U.S. threatens more action on Syria following last week's missile strikes. Secretary of State Rex Tillerson will meet with Russia's foreign minister in Moscow on Wednesday, and according to the State Department he will discuss the future of Syrian President Bashar al-Assad.

United Airlines: United Airlines has been dealing with a public relations disaster after videos showing a man being forcibly removed from a flight went viral. There was even more backlash online when CEO Oscar Munoz put out statements Monday defending the airline's actions, saying United had to "re-accommodate" the passenger. On Wednesday, Munoz apologized in an internal email with the subject line: "A message from Oscar: I’m sorry. We will fix this."

Winners and Losers:  United Airlines' stock closed 1 percent lower because of fallout from the overbooking scandal. At one point shares sunk 4 percent, but the stock recovered partially due to Munoz's apology.

Shares of online coupon site RetailMeNot Inc. skyrocketed 48 percent after news the company would be acquired by Harland Clarke Holdings Corp.

Apple continued its losing streak with shares closing 1 percent lower Tuesday.

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