U.S. stocks mostly fell on Friday, with the S&P 500 halting a four-session win streak that lifted it to a record, as investors weighed rising tension between Russia and Ukraine and speeches by European Central Bank President Mario Draghi and Federal Reserve Chair Janet Yellen.
Both central bankers gave the market what was expected, with Yellen reiterating that slack remains in the U.S. labor market even as the American economy continues a five-year recovery and Draghi expressing confidence that stimulus already announced and a weaker euro would help the euro-zone economy, but the ECB is ready to do more if needed.
"I don't think there was anything earth shattering out of her mouth, the labor market has gotten better," said Doug Foreman, chief investment officer at Kayne Anderson Rudnick.
"If anything the euro zone and Draghi are looking at easing further and providing more liquidity to support the European economy. The weaker economic data out of euro zone in the second quarter is probably a function of a decline in confidence, which has to do with geopolitical risks there," said Carin Pai, executive vice president and director of equity management at Fiduciary Trust.
Quantitative easing isn't out of the question from the ECB, as there is "more evidence that Europe is having trouble, and the Ukraine situation is definitely having an impact on them," Foreman added.
Stocks fell to session lows after NATO said it was observing an alarming increase in Russian forces near Ukraine and fluctuated after Yellen spoke, while churning mostly lower ahead of, and during, Draghi's remarks.
"The market is vulnerable to some sort of a pullback, as it basically has ignored geopolitical tensions building up," said Peter Cardillo, chief market economist at Rockwell Global Capital.
"Yellen basically said what she's been saying all along, that everything is subjective. She said pretty much what the market was expecting, but market had already discounted that in its previous sessions," added Cardillo.
Fed chair: Getting closer to objective, but still hard to gauge labor-market slack
The CBOE Volatility Index, a measure of investor uncertainty, dropped 2.5 percent to 11.47.
The euro strengthened against the U.S. dollar, which turned lower against the currencies of major U.S. trading partners; the 10-year Treasury yield held at 2.402 percent.
The euro zone has had more of an impact on U.S. yields because European yields have come down this year, which has made the U.S. bond market relatively attractive," said Pai at Fiduciary Trust.
Foot Locker rose after the athletic-shoe maker reported second-quarter earnings; Aeropostale fell a day after the teen-apparel retailer posted a loss for the second quarter. Home Depot tabbed retail-industry veteran Craig Menear as chief executive of the home-improvement retailer.
Speaking to CNBC ahead of Yellen's speech in Jackson Hole, Wyoming, St. Louis Fed President James Bullard stuck with his forecast for a late first-quarter rate hike next year by the Fed.
"The market should expect a rate hike in 2015, whether in the first, second or third quarter is irrelevant, the market is preparing for a rate hike," said Cardillo.
"I'm not worried about whether they raise rates in the first quarter, the second quarter or the third quarter. Am I going to sell Home Depot because of that? I don't really know how to invest on that. Companies in the U.S. are doing well. That's the bottom line, and that's why the market is up at all-time highs, despite all the hand wringing over macro events," said Foreman at Kayne Anderson Rudnick.
Tensions between Ukraine and Russia rose, as Reuters reported around 90 Russian aid trucks had entered Ukraine without permission from Kiev.
Major U.S. Indexes
Benchmark indices tallied a third week of gains, with the Dow and S&P 500 posting their biggest weekly jump since the week ending April 17.
The Dow Jones Industrial Average shed 38.27 points, or 0.2 percent, to 17,001.22, leaving it 2 percent higher for the week.
Energy led sector declines and consumer discretionary performed the best as the lost 3.97 points, or 0.2 percent, to 1,988.40, leaving it with a 1.7 percent weekly gain and about 4 points from its record close and within 7 points of its intraday record, both set Thursday.
The Nasdaq added 6.45 points, or 0.2 percent, to, 4,538.55, up 1.7 percent from the week earlier.
For every five stocks rising, less than nine declined on the New York Stock Exchange, where 521 million shares traded. Composite volume neared 2.3 billion.
On the New York Mercantile Exchange, gold futures for December delivery rose $4.80 to $1,280.20 an ounce, leaving it down 2 percent on the week; crude-oil futures for October shipment fell 31 cents to $93.65 a barrel.
On Thursday, U.S. stocks climbed, with the S&P 500 toppling another record, as investors embraced upbeat economic reports and looked to a dovish message from Federal Reserve Chair Janet Yellen when she talks about the labor market in Jackson Hole on Friday.
"Nothing is really trend changing; we're seeing positive economic data, as we have seen," Dave Roda, regional chief investment officer for Wells Fargo Private Bank, said of Thursday's economic reports, which cast better-than-expected lights on housing, jobs and factory activity.
Read MoreNear 2,000, S&P knocks out 28th record close of 2014
—By CNBC's Kate Gibson
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