S&P 500, Dow end lower after Ukraine tension escalates
The S&P 500 retreated from a record close it set on Thursday after Ukrainian officials said Russia had launched a "direct invasion" by sending a convoy of trucks across the border.
Investors had been hoping that Yellen would catapult the S&P to the milestone 2,000 level.
While Russia has maintained the trucks contain humanitarian aid, NATO Secretary General Anders Fogh Rasmussen condemned the move as an "alarming build-up." He called on Russia to "stop destabilizing Ukraine."
Markets were also pressured by comments from Jackson Hole, Wyoming, where Yellen and European Central Bank President Mario Draghi delivered remarks on the labor market. Yellen did not give a timeline for Fed interest rate hikes, saying that with slack remaining in the labor market, "there is no simple recipe for appropriate policy."
The Dow Jones industrial average fell 38.27 points, or 0.22 percent, to 17,001.22, the S&P 500 ended down 3.97 points, or 0.2 percent, at 1,988.4 and the Nasdaq Composite added 6.45 points, or 0.14 percent, to 4,538.55.
Despite the day's losses, all three major indexes posted gains for the week, with the Dow up 2 percent, the S&P up 1.7 percent and the Nasdaq up 1.6 percent. It was the strongest week of gains for both the Dow and the S&P since April, and the third straight week of gains for all three indexes.
Retailers moved higher, led by a 7.4 percent advance in Ross Stores to $74.37 after the apparel and home fashion retailer posted second-quarter results. The S&P retail index gained 0.6 percent, posting its best week since late February.
The Nasdaq Composite was lifted by Keurig Green Mountain, whose shares soared 13.3 percent to $133.36. The K-cup coffee-pod maker said earlier in the day it had inked a deal to make and sell Kraft Foods Group Inc's coffee.
About 4.1 billion shares traded on all U.S. platforms, according to BATS exchange data, compared with the five-day average of 5.1 billion.
European shares fell after a brisk two-week rally, hurt by a ratcheting-up of tensions in Ukraine, although traders said a dovish tone in a speech by US Federal Reserve Chair Janet Yellen limited losses.
The FTSEurofirst, which fell as much as 0.7 percent in a choppy day of trade, managed to recover some of its poise to end the session down 0.3 percent at 1,351.38 points.
Despite Friday's overall weakness, the FTSEurofirst recorded its biggest weekly gain in six months - up 2.1 percent.
The index has risen more than 4 percent since a low hit two weeks ago, regaining ground following a sell-off triggered in June by the worries over the crisis in Ukraine.
But even after the sharp two-week rally, the index is still down more than 3 percent from the 5-1/2 year high hit in June.
The euro zone's blue-chip Euro STOXX 50 index was down 0.8 percent at 3,098.50 points. In the first minutes of trading, the index tested a key resistance level representing its 200-day moving average, before falling back.