The owner of Chinese video-sharing service TikTok is undergoing a national security review of its purchase of the Musical.ly app, reports Reuters.
ByteDance bought Musical.ly for $1bn (£773m) in 2017.
Quoting unnamed sources, Reuters said the deal was being probed because it had not been cleared by a US body that scrutinises acquisitions.
The investigations comes amid growing US suspicion of Chinese tech firms' activity.
The Committee on Foreign Investment in the United States (CFIUS) has started to look at the Musical.ly deal, sources told Reuters.
The Committee has scope to look at the deal because it was not scrutinised when it was originally signed. The body reviews acquisitions by non-US firms to establish whether they affect or undermine national security.
The news service said CFIUS had "concerns" about what was going to be done with the assets ByteDance acquired when it bought Musical.ly. The social music app claimed to have 60 million active users a month at the time of the acquisition.
ByteDance has not commented on Reuters' news story.
The CFIUS investigation is also thought to have gained traction thanks to calls from US politicians to look at TikTok over its alleged censorship of political messages and how it handles user data.
TikTok has rebuffed the claims of Chinese government interference over content and said it "does not remove content" based on Chinese sensitivities.
Many American teenagers are keen users of TikTok - figures suggest 60% of the app's US users are aged between 16 and 24.
In a statement, TikTok said it could not comment on "ongoing regulatory processes" but added "we have no higher priority than earning the trust of users and regulators in the US".