Stocks headed lower in early trading Friday, dragged down by disappointing results out of retail giant Amazon and Ford. Escalating tensions between the U.S. and Russia over Ukraine also weighed on investors' minds.

KEEPING SCORE: The Standard & Poor's 500 index fell nine points, or 0.5 percent, to 1,870 as of 10 a.m. Eastern. The Dow Jones industrial average fell 111 points, or 0.7 percent, to 16,390 and the Nasdaq composite was down 41 points, or 1 percent, to 4,106.

Traders work on the floor of the New York Stock Exchange. Global stocks tumbled Friday April 25, 2014 after tensions over Ukraine mounted and S&P cut Russia's credit rating, warning of capital flight due to the crisis. (AP Photo/Richard Drew, File)

FORD STALLS: Ford fell 50 cents, or 3 percent, to $15.78 after the company reported earnings that fell short of Wall Street's expectations. Worldwide sales rose 6 percent in the first quarter, but the company reported a sales drop in North America that cut into the company's profit. General Motors fell 47 cents, or 1.5 percent, to $33.70.

AMAZON: Shares in Amazon, the world's largest online store, sank $29.50, or almost 9 percent, to $308.28. Amazon reported late Thursday an increase in first-quarter profit, but the company also said that spending on investments will likely lead to an operating loss in the second quarter.

RUSSIA: Secretary of State John Kerry accused Russia on Thursday of failing to live up to commitments it made to ease the crisis in Ukraine. In blunt language, Kerry said that unless Moscow takes immediate steps to de-escalate the situation, Washington will have no choice but to impose additional sanctions.

OTHER MARKETS: Prices for U.S. government bonds rose, pushing the yield on the 10-year note down to 2.67 percent from 2.68 percent late Thursday. Yields fall when bond prices rise. The price of oil slipped $1.32, or 1.3 percent, to $100.65.