The euro fell below $1.4300 for the first time since September 4, according to Reuters data, as investors bought the U.S. currency amid the Iran-Iraq tensions.
The dollar's advance led investors to pare risky bets, such as stocks, but the Nasdaq edged higher as upbeat results from Oracle and Research In Motion boosted optimism about technology spending.
Oracle shares rose 7 percent, while RIM's Nasdaq-traded shares jumped 9.7 percent.
I think we're seeing a continued flight to safety, said Tom Schrader, managing director of U.S. equity trading at Stifel Nicolaus Capital Markets in Baltimore.
The stronger the dollar gets it means investors will be unwinding the dollar carry trade and that's going to put upward pressure on the dollar and downward pressure on the stocks.
The U.S. dollar index <.DXY> climbed about 0.5 percent, a move that pressured shares of natural resource companies and weighed on exporters like Caterpillar Inc , which pared some losses after falling nearly 2 percent.
The Dow Jones industrial average <.DJI> was down 10.96 points, or 0.11 percent, at 10,297.30. The Standard & Poor's 500 Index <.SPX> was up 2.00 points, or 0.18 percent, at 1,098.08. The Nasdaq Composite Index <.IXIC> was up 17.79 points, or 0.82 percent, at 2,197.84.
U.S. Treasury debt prices fell as profit-taking emerged after a safe-haven rally in bond markets on Thursday that was ignited by falling stocks and concerns about Greece's fiscal problems.
But renewed weakness on Wall Street curbed the decline in bond prices in the absence of major U.S. economic data.
It looks to me like things are going in contrary directions, said Jerry Webman, chief economist at Oppenheimer Funds in New York.
Everybody is trying to ask if there really is some of sort of synchronized global recovery, the answer to which I think is 'yes,' Webman said. And we now expect there to be bubbles somewhere. So where is the next bubble? Is it gold, some emerging market commodity or say currency or equity market?
European shares closed lower, with banks falling as ongoing concerns about tough new Basel regulations weighed and oils down after crude prices retreated.
The FTSEurofirst 300 <.FTEU3> index of leading European shares closed 0.5 percent lower at 1,013.15.
Oil rose above $73 a barrel amid the oilfield tensions, while the stronger dollar showed investors remain wary of risky commodities. Gold retreated toward $1,100 an ounce before reversing course, and copper prices eased as the dollar firmed against the euro.
Spot gold prices rose $14.80 to $1112.60 an ounce.
Iraq's Deputy Interior Minister said Iranian troops were still occupying an Iraqi oil well. Iraq hasn't taken any military action but officials alleged repeated Iranian incursions into its territory this week.
The Iraq-Iran issue is bringing some nervousness in the market, but I think there is a very high possibility that there is nothing in the story, said Eugen Weinberg, oil analyst at Commerzbank in Frankfurt.
If there is some sort of conflict, then the price reaction is too small but if it is nothing the reaction is too high, Weinberg added.
U.S. light sweet crude oil rose 70 cents to $73.35 a barrel.
The dollar was up against a basket of major currencies, with the U.S. Dollar Index <.DXY> up 0.36 percent at 77.972.
The euro was down 0.37 percent at $1.4291. Against the yen, the dollar was up 0.71 percent at 90.52.
The benchmark 10-year U.S. Treasury note was down 10/32 in price to yield 3.52 percent.
The MSCI index of Asia Pacific stocks traded outside Japan <.MIAPJ0000PUS>, which has rallied more than 60 percent this year, was 0.5 percent lower. In Japan, the Nikkei share index <.N225> dipped 0.2 percent, paring most of the day's losses.
(Reporting by Ellis Mnyandu, Nick Olivari and Richard Leong in New York; Joe Brock and Joanne Frearson in London; writing by Herbert Lash; Editing by Kenneth Barry)