Federal Reserve Chair Janet Yellen said the U.S. is on track for more interest rate hikes and brushed off last week's dismal May jobs numbers, but didn't provide any clues on the timing of the next liftoff, according to a speech on Monday in Philadelphia. 'I continue to think that the federal funds rate will probably need to rise gradually over time to ensure price stability and maximum sustainable employment in the longer run,' she said. Yellen also downplayed last week's dismal May jobs report. The economy created only 38,000 jobs in May, missing estimates of 158,000. 'Although this recent labor market report was, on balance, concerning, let me emphasize that one should never attach too much significance to any single monthly report. Other timely indicators from the labor market have been more positive.' TheStreet's Scott Gamm reports from Wall Street.