U.S. stock markets posted their heaviest losses in two years Friday.

Analysts said several factors caused investors to sell off their stocks.

They said oil prices rose to more than 68 dollars a barrel because of worries about the stability of oil supplies from Iran and Nigeria.

Two large U.S. companies, General Electric and Citicorp added to investors' concern by posting lower than expected profits.

And shares of Internet search company Google dropped after the U.S. government filed suit to force it to turn over data accumulated about its users.

Each of the major U.S. stock indexes, the NASDAQ, Dow Jones and the S & P 500 lost about 2 percent of value.

Some information for this report was provided by Bloomberg.