* Indexes cut early gains on geopolitical concerns
* Apple rallies, announces 7-for-1 stock split
* Caterpillar gains after results; Verizon, 3M fall
* Indexes down: Dow 0.2 pct, S&P 0.1 pct, Nasdaq 0.1 pct
(Updates to open)
NEW YORK, April 24 (Reuters) - U.S. stocks were flat in volatile trading on Thursday, with indexes cutting early gains on a resurgence of concerns related to Ukraine, though Apple jumped following its results.
Markets had opened higher, with the Nasdaq especially gaining on the back of strong tech results. However, indexes turned negative in the first half-hour of trading after Russian Defense Minister Sergei Shoigu said Russia started military drills near the border with Ukraine.
The issue "is a lit stick of dynamite" with remote chances of a peaceful resolution, said Todd Schoenberger, managing partner at LandColt Capital in New York. "All those geopolitical concerns warrant instability and higher commodity prices, and both of those are things Wall Street hates."
Apple Inc, the most valuable U.S. company by market capitalization, rose 7.5 percent to $563.89 a day after posting revenue that far outpaced expectations, helped by strong iPhone sales. It also approved another $30 billion stock buyback plan, raised its dividend and authorized a seven-for-one stock split.
"People have been critical of the cash on Apple's balance sheet, but now it has faced up to that criticism. It's doing all the right things, and I don't think a move over $600 would be out of place now," said Michael Binger, senior portfolio manager at Gradient Investments LLC in Minneapolis, which owns Apple.
Caterpillar Inc rose 2.5 percent to $106.01 after reporting better-than-expected earnings and raising its full-year profit view. On the downside, both Verizon Communications Inc and 3M Co fell after results missed expectations. Verizon dropped 1.7 percent to $46.60 and 3M fell 1.4 percent to $136.11.
The Dow Jones industrial average was down 31.08 points, or 0.19 percent, at 16,470.57. The Standard & Poor's 500 Index was down 1.87 points, or 0.10 percent, at 1,873.52. The Nasdaq Composite Index was down 7.74 points, or 0.19 percent, at 4,119.23.
Social media giant Facebook Inc posted a 72 percent jump in first-quarter revenue, lifted by its mobile advertising business. After opening sharply higher, the stock pared its gains, last trading down 0.5 percent at $60.93.
Strong earnings have lifted the S&P 500 for six of the past seven sessions, though companies have largely been beating reduced forecasts. According to Thomson Reuters data, profits are seen rising 1.6 percent this quarter, down from the 6.5 percent growth rate estimated at the start of the year, according to Thomson Reuters data.
A number of cloud-computing stocks, which have struggled lately but rose last week, opened higher and then quickly sold off. Workday Inc fell 6.6 percent while Salesforce.com was off 3.7 percent at $53.60.
Zimmer Holdings Inc agreed to buy Biomet Inc in a deal valued at about $13.35 billion to broaden its portfolio of products that treat bone and joint-related disorders. Zimmer rose 15.5 percent to $105.69.
Sina Corp fell 7.4 percent to $49.31 after Chinese state media reported the company had been stripped of its online publication license after being targeted in a pornography crackdown.
(Editing by Chizu Nomiyama and Nick Zieminski)