US Federal Reserve chief Janet Yellen said Thursday that she still expects to increase interest rates in 2015 and that concerns about weaker global growth likely will not affect that plan.

Yellen said improvements in the US economy "will likely entail an initial increase in the federal funds rate later this year."

Policymakers will continue to monitor weaker activity overseas, she said, but the impact will probably not be "large enough to have a significant effect on the path for policy."