NEW YORK | Stocks headed lower in midday trading Friday, dragged down by disappointing results from retail giant Amazon and Ford. Escalating tensions between the U.S. and Russia over Ukraine also weighed on the market.

KEEPING SCORE: The Standard & Poor's 500 index fell 10 points, or 0.5 percent, to 1,868 as of 12:17 p.m. Eastern. The Dow Jones industrial average fell 106 points, or 0.6 percent, to 16,395 and the Nasdaq composite fell 52 points, or 1.3 percent, to 4,096.

FORD STALLS: Ford fell 52 cents, or 3.2 percent, to $15.80 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 23 cents, or 1 percent, to $33.94.

AMAZON PRICE CUT: Amazon, the world's largest online store, sank $28.90, or 9 percent, to $308.25. 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.

VOLATILITY: Investors have had little patience for companies missing their forecasts this quarter, said Scott Clemons, chief investment strategist at Brown Brothers Harriman.

"The market is in a precarious position at the moment, and overreacts to bad news far more than it did last year," he said, noting as an example the 10 percent drop in Amazon's stock price, even though the company meet analysts' forecasts. "This volatility doesn't have to be the enemy, because it allows you to pick up companies on the cheap."

START IT UP: Microsoft rose 39 cents, or 1 percent, to $40.24. In its first quarter under new CEO Satya Nadella, the software giant reported a profit of 68 cents per share, five cents better than what analysts had expected. Investors generally have been impressed with Nadella since he took over the company Feb. 5. Microsoft shares have risen 12 percent since his appointment, compared the 7 percent rise in the S&P 500 in the same period.

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 2.66 percent from 2.68 percent late Thursday. Yields fall when bond prices rise. The price of oil slipped $1.14, or 1.1 percent, to $100.81.