U.S. stocks open lower on uncertainty over Greece

U.S. stocks opened lower on Wednesday, as concerns over Greece still weighed on investor sentiment.

Greece's government pledged on Wednesday the immediate implementation of reforms as soon as next week in exchange for further support via the European Stability Mechanism (ESM) to avoid default and Grexit, according to the formal request tabled, a Finance Ministry statement said.

A deal to tackle the Greek debt crisis should be sealed by the end of this week, Greek Prime Minister Alexis Tsipras said Tuesday night after a eurozone summit in Brussels.

An emergency Eurogroup meeting in Brussels, Belgium, on the Greek debt deal ended inconclusive Tuesday afternoon, with lenders saying publicly that their expectation for new Greek proposals fell, but Athens denied.

The finance ministers of eurozone countries didn't receive new proposals they had expected from Greece Tuesday, said Eurogroup head Jeroen Dijsselbloem after the crucial meeting.

Greek banks are closed and capital controls have been imposed in Greece since June 29. ATMs are expected to run out of cash this week, and without emergency assistance, Greece seems to be heading to default and possibly an exit from the eurozone.

The Federal Open Market Committee (FOMC) minutes will also be in focus, as traders will scan the Fed' s June report for hints on the timing of an interest rate hike.

Shortly after the opening bell, the Dow Jones Industrial Average shed 124.16 points, or 0.70 percent, to 17,652.75. The S&P 500 was down 13.11 points, or 0.63 percent, to 2,068.23. The Nasdaq Composite Index lost 33.25 points, or 0.67 percent, to 4,964.21.

U.S. stocks pared early losses to end mildly higher Tuesday, as investors were assessing the impacts of the unfolding Greek debt crisis. Endi