* Wall Street mostly rises, gains accelerate in late trading
* Yellen says U.S. economy still needs support
* Putin comments on Ukraine suggest easing tensions
* Gold prices decline, U.S. dollar index edges up (Updates to close of U.S. trading)
By Ryan Vlastelica
NEW YORK, May 7 U.S. stocks mostly rose on Wednesday, adding to their gains in late trading after Federal Reserve Chair Janet Yellen indicated continued central bank support for the U.S. economy, while stocks in other regions were flat.
Many other markets closed before the acceleration in U.S. gains. Equities were volatile throughout the day, with investors parsing comments from Russian President Vladimir Putin indicating a possible easing to the geopolitical concerns over Ukraine that have weighed on markets.
Gold, viewed as a safe-haven asset, fell 1.4 percent, while the U.S. dollar rose slightly against a basket of currencies, though it remained near a six-month low.
Yellen said the U.S. economy was still in need of support from the central bank given the "considerable slack" in the labor market. She also cited the housing sector and geopolitical tensions as issues of concern.
Putin said he was ready to discuss a way out of the Ukrainian crisis and called on separatists in east Ukraine to postpone a May 11 referendum on the status of the mostly Russian-speaking region.
"We need confidence that the Russia situation remains isolated; getting that would do a lot to stabilize the market. Of course, anything that suggests more escalation is on the way would be a real negative," said Eric Green, senior portfolio manager at Penn Capital Management in Philadelphia.
The Dow Jones industrial average ended up 117.52 points, or 0.72 percent, at 16,518.54. The Standard & Poor's 500 Index was up 10.49 points, or 0.56 percent, at 1,878.21. The Nasdaq Composite Index was down 13.09 points, or 0.32 percent, at 4,067.67.
The Nasdaq was pressured by Whole Foods Market Inc, which plummeted 19 percent to $38.93 on disappointing results, and by Yahoo Inc, which lost 6.6 percent at $34.07. The Dow gained on strength in UnitedHealth Group, which added 3.5 percent following positive results from peer company Humana Inc.
The benchmark 10-year U.S. Treasury note was up 1/32, the yield at 2.5896 percent. The U.S. dollar index rose 0.2 percent against a basket of currencies. The euro fell 0.1 percent against the dollar while the yen dipped 0.2 percent against the dollar.
European shares edged up 0.1 percent after trading lower earlier in the session. The MSCI International ACWI Price Index was flat.
Oil prices rose, underpinned by the tensions in Ukraine, though Brent's premium over U.S. prices narrowed after an industry report showed a sharp draw in inventories in the world's largest oil consumer. U.S. crude futures rose 1.2 percent to $100.50 while Brent crude was up 1 percent. (Editing by Dan Grebler)