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US stocks on edge as eyes fix on Yellen

U.S. stock index futures signaled a flat open on Tuesday, as investors await hints on the timing of an interest rate rise at Fed Chair Janet Yellen's speech to Congress.

Yellen's semi-annual testimony the Senate Banking Committee in Washington is due at 10.00 a.m. ET. Investors will be looking closely for further clarification as to when the Fed may start raising interest rates, having shifted their language from referencing a "considerable period" to them being "patient."

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Federal Reserve Board Chairwoman Janet Yellen testifies before the Senate Banking, Housing and Urban Affairs Committee July 15, 2014 in Washington, DC.
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On the data front, the release of February's consumer confidence index at 10.00 a.m. ET should also attract attention, with expectations for a retreat from the previous month's post-crisis high.

The S&P/Case-Shiller composite index of home prices in 20 cities increased by 4.5 percent in December from the same period last year. The Richmond Fed's manufacturing index for February at 10.00 a.m. ET.

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Macy's reported earnings for the holiday quarter that missed analyst estimates.

Home Depot posted fourth-quarter earnings excluding items of $1.00 per share, up from 73 cents a share in the year-earlier period, beating analysts' expectations. Revenue increased to $19.2 billion from $17.7 billion a year ago.

Analysts had expected the company to report earnings of 89 cents a share on $18.7 billion in revenue, according to a consensus estimate from Thomson Reuters. Same-store sales rose 7.9 percent in the quarter.

Home builder Toll Brothers easily topped estimates on earnings and revenue as the firm sold more homes at higher prices. Toll earned 44 cents per share for its first quarter, well above estimates of 30 cents.

Comcast, the NBCUniversal parent, earned an adjusted 77 cents per share for the fourth quarter, 1 cent below estimates, though revenue was above Street forecasts. Comcast raised its annual dividend by 11 percent to $1 per share and increased its share repurchase authorization to $10 billion.

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Hewlett-Packard, Lending Club, Boston Beer, Dreamworks Animation, First Solar, La Quinta and Newfield Exploration are due after the bell.

In oil markets, Brent crude futures dropped to 59.37 a barrel on Tuesday and U.S. crude was back at $49.62 a barrel after climbing above $50 on Tuesday afternoon, after doubts were raised over an anticipated cut in production from the Organization of the Petroleum Exporting Countries (OPEC).

Futures moved little on the news before the bell that a four-month bailout extension for Greece.

The country sent its economic reform plans—which include measures to crack down on tax evasion and corruption—to the euro zone overnight.

In Europe, equities were mixed on Tuesday, ahead of Yellen's testimony and resolution in Greece.

CNBC's Peter Schacknow contributed to this report.