Stocks closed sharply lower Friday, with the Dow Jones Industrial Average turning negative for 2006 and posting its biggest one-day loss since March 2003, after oil prices hit a four-month high and General Electric Co. and Citigroup Inc. disappointed with their fourth-quarter earnings.

For the week, the Dow lost 2.67 percent, the S&P 500 was down 2.03 percent and the Nasdaq declined 2.99 percent.

GE said its fourth-quarter profit tumbled 46 percent after absorbing nearly $3 billion of losses from selling most of its insurance business. Excluding items, the results matched Wall Street estimates but failed to inspire investors. GE sank $1.31 to $33.37.

Citigroup’s earnings jumped 30 percent from strength overseas and a gain on the sale of its asset-management unit. However, its profit before one-time items was slightly weaker than forecast, sending shares down $2.25 to $45.69.