Despite uncertainty over Syria and a disappointing jobs report at the week's close, all three leading indices posted gains for the holiday-shortened week.
The Dow Jones Industrial Average rose 112.19 (0.76 per cent) to 14,922.50. The broad-based SP 500 advanced 22.20 (1.36 per cent) to 1,655.17, while the tech-rich Nasdaq Composite Index tacked on 70.14 (1.95 per cent) at 3,660.01.
Markets were closed on Monday for the Labor Day holiday.
The week's gains were a big improvement over August, which saw the steepest monthly declines for the Dow and SP 500 since May 2012.
Perhaps the week's biggest bright spot was US August auto sales, with the industry selling 17 per cent more cars than a year ago. General Motors, Ford and Chrysler all posted double-digit gains.
The robust auto sales lifted stocks on Wednesday and 'spilled over into better sentiment in general,' said Michael James, managing director of equity trading at Wedbush Securities.
Markets also digested Monday's news that Verizon would buy out Vodafone's 45-per cent stake in their Verizon Wireless joint venture for $US130 billion ($A143.16 billion). Verizon plans a record $US25 billion debt offering associated with the deal in the next week or two, a person close to the situation said.
On Tuesday, Microsoft turned heads when it announced a $7.2 billion acquisition of Nokia's handset business in a bid to become a bigger player in the smartphone business.
Some analysts see increased merger and acquisition activity as a sign of rising confidence in the economy.
Analysts were also cheered by an invitation from Apple announcing a September 10 event in California. The gathering is widely expected to launch two new versions of the iPhone, including a less expensive model expected to appeal to China and other emerging markets.
On Friday, The Wall Street Journal reported that Apple was preparing to ship iPhones to China Mobile in a long-anticipated deal. Apple closed the week 2.3 per cent higher at $498.22.
The news on autos, telecommunications and Apple helped offset Friday's disappointing jobs report. The Labor Department reported a gain of 169,000 jobs in August, below the 177,000 projected by analysts. The report also slashed the jobs estimates for June and July.
The report, while 'not a disaster,' was weak enough to suggest that the Federal Reserve will either delay its plans to taper its bond-buying program, or reduce the program even more gradually than previously thought, said William Lynch, director of investment at Hinsdale Associates.
'I don't think the economy, as sluggish as it is, can take too much in the way of tapering,' Lynch said.
Investors are also skittish over the Obama administration's efforts to launch a military strike on Syria in response to Syria's purported use of chemical weapons.
Crude oil prices Friday pushed to a 28-month high of $US110.53 in New York amid US-Russian tensions over Syria. But equity markets have reacted inconsistently to Syria news, sometimes dropping in recent weeks on Syria headlines, and sometimes not.
'Of all the risks out there, the one that has the highest probability to hurt the market in the near term is the Middle East situation,' said Scott Wren, senior equity strategist at Wells Fargo Advisors.
'The market's not as focused on it as I think it probably ought to be.'
Congressional debate on Syria is expected to dominate next week's news. The economic calendar is relatively light, with August retail sales and inflation data due on Friday.
The calendar also includes a September 12 meeting with Securities and Exchange Commission Chair Mary Jo White and leading exchanges in the wake of the August 22 outage at Nasdaq Stock Market caused by a tech glitch.
Anthony Conroy, a trader at BNY Convergex Group, predicted the market would trade in a 'tight range until we get more clarity on the Fed and more clarity on Syria.'