(Reuters) - The U.S. Department of Justice plans to focus an upcoming lawsuit against TikTok on allegations that the popular social media platform violated the privacy rights of children, rather than claims it misled adult users about its data privacy practices, according to a source familiar with the matter.

The U.S. Federal Trade Commission investigated the potential violations by TikTok and its parent company ByteDance and referred the case to the Justice Department on Tuesday.

"The investigation uncovered reason to believe named defendants are violating or are about to violate the law and that a proceeding is in the public interest," the FTC said in a statement at the time.

Reuters in 2020 first reported the FTC and the U.S. Justice Department were looking into allegations the popular social media app failed to live up to a 2019 agreement aimed at protecting children's privacy.

TikTok has said it strongly disagrees with the FTC's allegations and is disappointed the agency decided to pursue a lawsuit.

The probe is separate from ongoing concerns in Congress about the potential that the data of TikTok's 170 million U.S. users could be improperly accessed by the Chinese government.

TikTok denies the allegation.

TikTok is challenging a law passed in April that requires its Chinese-parent ByteDance to divest TikTok's U.S. assets by Jan. 19 or face a ban.

ByteDance said in the case on Thursday that a ban would be inevitable without court intervention, and that a divestiture is "not possible technologically, commercially, or legally."