Futures Tumble as Greece Worries Continue

U.S. stock index futures fell sharply Tuesday amid renewed concerns that Greece and its private bondholders would not meet the deadline to complete a debt swap and ahead of the Super Tuesday primaries.

With no major economic reports on tap, developments in Europe will remain in focus.

European shares fell in early trade on continued concerns about the forthcoming Greek debt swap deal. The bond swap plays an important role of a second bailout loan for the debt-ridden nation that aims to keep it from defaulting. It faces a bond redemption on March 20.

Meanwhile, strategists have been worrying over Wall Street's recent rally starting to lose steam. The S&P 500 has dropped 0.7 percent over the last two sessions, while the Nasdaq has erased 1.3 percent.

Among techs, Apple edged lower even after Barclays raised its target price on the iPad maker to $710 from $630.

Google and Yahoo also slipped even after Nomura started coverage of the Internet companies with "buy" and "neutral" ratings and price targets of $750 and $13.50, respectively.

Skullcandy plunged after the headphone maker said CFO Mitch Edwards has resigned.

Internet radio company Pandora is scheduled to post earnings after-the-bell tonight.

The biggest day of voting to decide which Republican candidate will challenge President Obama in the November 6 election is likely to dominate the news agenda.

Obama will hold his first news conference of the year at 1:15 p.m. ET, with the economy and Middle East tensions expected to be prominent topics.

—Follow JeeYeon Park on Twitter: @JeeYeonParkCNBC

On Tap This Week:

TUESDAY: Earnings from Pandora
WEDNESDAY: Weekly mortgage apps, Challenger job-cut report, ADP employment report, productivity & costs, oil inventories, consumer credit; Earnings from American Eagle, Hovnanian, H&R Block
THURSDAY: Jobless claims, quarterly services survey; Earnings from Smithfield Foods, Aeropostale
FRIDAY: Non-farm payrolls, international trade, wholesale trade; Earnings from Ann

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