Global shares tumble as Greek deal falters

The S&P 500 posted its biggest daily percentage decline thus far in 2012 after an about-face on Greece's long-awaited debt deal ended a five-week streak of gains for equities.

The Dow Jones industrial average was down 89.23 points, or 0.69 percent, at 12,801.23. The Standard & Poor's 500 Index was down 9.31 points, or 0.69 percent, at 1,342.64. The Nasdaq Composite Index was down 23.35 points, or 0.80 percent, at 2,903.88.

European shares fell today, dragged lower by banks on concerns about the outcome of the euro zone debt crisis after finance ministers imposed further conditions before approving a rescue package for Greece.

Greek political leaders said they had clinched a deal on economic reforms needed to secure a second EU bailout, but euro zone finance ministers demanded more steps and a parliamentary seal of approval before providing the aid.

The FTSEurofirst 300 index of top European shares was down 0.5 percent at 1,068.09 points.

The STOXX Europe 600 euro zone Banking Index, exposed to the euro zone's sovereign debt, fell 1.1 percent. The index is still up more than 19 percent in 2012.

"As Greece moves towards a final resolution, you'll see some nervousness, I don't think that's necessarily a reason to be selling but you might sit on the sidelines and wait for the next news to come through. Use the volatility," Urquhart Stewart said.

Meanwhile, Japan's Nikkei share average edged below 9,000 today as caution prevailed on Greece even after leaders in Athens clinched a long-delayed bailout deal, but euro zone finance ministers urged the country to commit to more reforms.

The Nikkei dipped 0.6 percent to 8,947.17, with the 200-day moving average near 9,057 acting as resistance. The benchmark has still managed to rise 1.3 percent this week. The broader Topix eased 0.7 percent to 779.07.