* Major indexes on track for second week of gains
* Microsoft shares rise after results, Amazon down
* Investors concerned over fallout to Ukraine violence
* Futures down: Dow 33 pts, S&P 4.8 pts, Nasdaq 13.25 pts
By Ryan Vlastelica
NEW YORK, April 25 (Reuters) - U.S. stock index futures edged lower on Friday as intensifying violence in Ukraine and weakness in Amazon.com overshadowed positive results from Microsoft Corp.
* In the latest sign of ongoing geopolitical strife, Ukrainian forces killed up to five pro-Moscow rebels and Russia launched army drills near the border in response, raising fears its troops would invade. Separately, local police said seven people were injured overnight at a pro-Ukrainian checkpoint near the Black Sea port of Odessa when an explosive device blew up.
* While the situation has taken a backseat to corporate earnings in recent weeks, investors remain on edge over what the potential fallout could be to any prolonged tension or violence.
* Amazon fell 2 percent to $330.25 after posting a jump in revenue that was offset by sharp increases in spending. On the upside, Microsoft's earnings topped analyst forecasts, while investors were cheered by the software giant's new emphasis on mobile and cloud computing. Shares rose 1.7 percent to $40.52.
* S&P 500 futures fell 4.8 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 fell 33 points and Nasdaq 100 futures fell 13.25 points.
* For the week, the Dow is up 0.6 percent, the S&P is up 0.7 percent and the Nasdaq is up 1.3 percent. It is the second straight week of gains for all three, boosted by strong results, especially from high-profile names like Apple Inc and Caterpillar Inc.
* While companies are beating a lowered bar, estimates have been improving. Profits are seen rising 2.9 percent this quarter, down from the 6.5 percent growth rate estimated at the start of the year, but above the low of 0.6 percent seen last week, according to Thomson Reuters data.
* Ford Motor Co fell 2.5 percent to $15.91 in premarket trading after the company reported results, while Whirlpool Corp reported adjusted earnings that rose from the prior year, and revenue that was up 4.7 percent.
* Visa Inc, the world's largest credit and debit card company, said U.S. sanctions on Russia were hurting its card transaction volumes and that revenue growth would slow further this quarter.
* According to sources familiar with the matter, Allergan Inc approached Shire Plc in recent months about a possible takeover but was rebuffed, in the latest example of a U.S. drugmaker seeking to buy an overseas rival to lower its tax rate. (Editing by Chizu Nomiyama)
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