WASHINGTON The United States has concerns about issues over privacy and social media, and the matter involving TikTok is not yet resolved, U.S. Treasury Secretary Janet Yellen told CNBC in an interview on Monday.

Yellen declined to discuss details involving the short video platform owned by Chinese parent company ByteDance, citing pending legal action that prevents U.S. regulators from acting.

"We do have concerns around the potential issues with privacy and social media," she said, adding that she cannot discuss TikTok specifically. "This is a matter that has not yet been resolved."

"This wasn't an explicit matter of discussion" between U.S. President Joe Biden and Chinese President Xi Jinping when they met last week, Yellen told CNBC.

She said she discussed Chinese investments in the United States with her Chinese counterpart during their own meeting, including the process involving the Committee on Foreign Investment in the United States (CFIUS).

CFIUS is an interagency committee, chaired by the Department of Treasury, which reviews foreign investments in U.S. businesses and real estate that implicate national security concerns.

Yellen added that both the Washington and Beijing recognize that they have the opportunity to work together after the presidents' met last week.

(Reporting by Doina Chiacu and Susan Heavey; Editing by Toby Chopra and Doina Chiacu)