U.S. Federal Reserve Board Chairwoman Janet Yellen spoke Thursday in Amherst, Massachusetts. Pictured: Yellen speaks during a past hearing in Washington, D.C. Reuters

UPDATE 6:45 p.m. EDT: The Secret Service announced that Fed Chairwoman Janet Yellen said she was doing OK after feeling lightheaded while delivering a speech in Amherst, Massachussets, on Thursday evening, CNBC tweeted.

UPDATE 6:35 p.m. EDT: Fed Chairwoman Janet Yellen was receiving medical attention Thursday after struggling to deliver a speech at the University of Massachusetts at Amherst, coughing and stopping to recompose herself several times before walking off stage, Reuters reported.

Yellen, who had been speaking for roughly an hour, appeared to lose her place in reading the speech and stopped several times. She abruptly said, "I think I will end here."

Original story:

AMHERST, Massachusetts (Reuters) -- Federal Reserve Chairwoman Janet Yellen said on Thursday she expects the U.S. central bank to begin raising interest rates later this year as long as inflation remains stable and the U.S.economy is strong enough to boost employment. Yellen, speaking a week after the Fed delayed a long-anticipated rate hike, said she and other Fed policymakers do not expect recent global economic and financial market developments to significantly affect the centra bank's policy.

Much of the recent inflationary weakness is due to special and likely temporary factors such as a strong dollar and low oil prices, she said, allowing U.S. inflation to rise to a 2-percent goal over the next few years.

She and the policy-making Federal Open Market Committee (FOMC) expect the world's largest economy to be strong enough to achieve maximum employment and to keep expectations for prices stable, she said.

"Most FOMC participants, including myself, currently anticipate that achieving these conditions will likely entail an initial increase in the federal funds rate later this year, followed by a gradual pace of tightening thereafter," Yellen said in prepared remarks at the University of Massachusetts, Amherst.

As it stands, she said, U.S. economic prospects "generally appear solid."