Wall Street falls after Greek debt downgrade

U.S. stocks fell to session lows on Tuesday after the credit ratings for both Greece and Portugal were cut, intensifying worries over their sovereign debt.

* The CBOE Volatility Index <.VIX>, known as Wall Street's fear gauge, jumped 17 percent following the downgrade of Greek ratings into junk territory.

* The Dow Jones industrial average <.DJI> dropped 146.61 points, or 1.31 percent, to 11,058.42. The Standard & Poor's 500 Index <.SPX> lost 19.30 points, or 1.59 percent, to 1,192.75. The Nasdaq Composite Index <.IXIC> gave up 34.53 points, or 1.37 percent, at 2,488.42.

(Reporting by Leah Schnurr; editing by Jeffrey Benkoe)