US stock futures fall on Ukraine-Russia tensions

U.S. stock-index futures declined on Friday amid heightened tensions between Russia and Ukraine and as investors await speeches by Federal Reserve Chair Janet Yellen and European Central Bank President Mario Draghi.

Foot Locker rose in early New York trading after the maker of athletic shoes reported second-quarter earnings; Aeropostale fell a day after the teen-apparel retailer posted a loss for the second quarter. Home Depot tabbed retail-industry veteran Craig Menear as chief executive of the home-improvement retailer.

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Speaking to CNBC ahead of Yellen's speech in Jackson Hole, Wyoming, St. Louis Fed President James Bullard stuck with his forecastfor a late first-quarter rate hike by the Fed.

After minutes from the latest Fed policy meeting, published Wednesday, were more hawkish than some expected, market watchers are keen to discover whether Yellen will alter her usual dovish tone.

It comes as geopolitical tensions between Ukraine and Russia heightened once again, as Reuters reported that around 90 Russian aid trucks had entered Ukraine without permission from Kiev.

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Dovish display?

Yellen is expected to start her speech at 10 a.m. Eastern at a meeting of central bankers in Jackson Hole, Wyoming.

"With the focus on labor markets, some are thinking she may take a less hawkish line that was evident in the FOMC (Federal Open Market Committee) minutes yesterday, as this is more her area of expertise and it is the labor market that has kept U.S. policy so accommodative for such a sustained length of time," Simon Smith, chief economist at FXPro, said in a morning note.

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The minutes of the FOMC's July meeting showed officials discussed raising interest rates sooner, but continued to disagree on how much the labor market is improving.

Deutsche Bank economists led by Colin Tan noted that the Jackson Hole meeting was unlikely to serve as a precursor for any shifts in monetary policy, but added: "The tone of Yellen's speech may still have a market impact and set the mood for busier times ahead in September."

"Given markets are seemingly expecting nothing but another dovish display from Yellen the risk is perhaps skewed to the other side," they wrote on Friday.

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Later in the day, the ECB's Draghi will also speak at Jackson Hole,

In Europe, shares were slightly lower as investors await Draghi's comments in particular, but also kept an eye on Ukraine. The market is looking for Draghi to explain whether Europe will carry out its own version of quantitative easing, or asset purchases, as data in the region continues to show signs of a recovery at risk of losing steam.

While in Asia, indices traded higher on Friday, following a positive lead from Wall Street on Thursday.