Updated at 10:35 a.m. ET: Stocks moved lower in choppy trading Monday as investors awaited signs of central bank stimulus and as Apple surged following a court victory.
News the European Central Bank was considering setting yield-band targets in a new bond-buying program that could help contain euro zone borrowing costs lifted positive sentiment on Friday, but many questions remain about the timing and size of any possible action.
Investors are looking ahead to a meeting of central bankers at Jackson Hole, Wyoming, on Friday for clarity on what the U.S. Federal Reserve and European Central Bank will do to support an economy showing signs of slowing growth.
Equities have rallied on growing expectations for a third round of quantitative easing from the Fed, and the news from Jackson Hole could determine whether the recent rally that took the S&P index to four-year highs will persist.
"Upcoming market movement will all come on QE3 and how likely it seems that we'll get it," said Robert Pavlik, chief market strategist at Banyan Partners LLC in New York. "The market has been expecting it, and we could react negatively if we don't."
Apple Inc gained after the company won a sweeping victory in a patent lawsuit against Samsung Electronics. Samsung said it would contest the verdict, which orders it to pay $1.05 billion in damages.
U.S.-listed shares of Nokia Corp, a Samsung competitor, surged.
"This should give Apple that much more power and strength in the market, which should obviously be a positive for the stock," said Pavlik. Shares of Apple have already gained about 64 percent so far this year.
Energy shares will be in focus on Monday, with crude oil advancing 0.8 percent on concerns a tropical storm in the Gulf of Mexico could suspend U.S. production.
In merger news, car rental firm Hertz Global Holdings said it would buy smaller rival Dollar Thrifty Automotive Group for about $2.3 billion while M&T Bank Corp is buying Hudson City Bancorp Inc for $3.7 billion.
Tiffany & Co climbed after reporting its second-quarter results, though it also cut its full-year profit and sales outlook.
European shares edged slightly higher, though trading volume was extremely light with the UK market shut for a bank holiday.
Over the weekend, German Chancellor Angela Merkel tried to play down comments from the Bundesbank, which compared the ECB's bond-buying program to a dangerous drug, as well as comments from an ally who said Greece should leave the euro zone.
Wall Street rose on Friday on news of the European bond-buying program, though a six-week string of gains in the S&P and Dow ended amid shifting expectations for central bank stimulus.
Reuters contributed to this report.
