U.S. stocks open higher after Yellen's comments

U.S. stocks opened higher Friday after U.S. Federal Reserve Chair Janet Yellen reiterated the strength of the country's economy.

Shortly after the opening bell, the Dow Jones Industrial Average rose 90.81 points, or 0.52 percent, to 17,632.77. The S&P 500 added 10.28 points, or 0.50 percent, to 2,052.19. The Nasdaq Composite Index gained 32.24 points, or 0.66 percent, to 4,880.60.

In a panel discussion with three former Fed chairs late Thursday, Yellen said she "certainly wouldn't describe this as a bubble economy," noting a healing labor market and a five-percent headline unemployment rate.

The global economy has seen relatively weak growth despite positive signs in the United States, she added.

Meanwhile, New York Fed President William Dudley said early Friday that a cautious and gradual approach to rate hikes is appropriate, citing risks to the U.S. economy remain tilted to the downside.

Investors were also encouraged by a strong rebound in oil prices, which surged some 5 percent in the early trading Thursday on fresh hopes over a proposed freeze in oil production. Endi