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Popular social media app TikTok has agreed to pay $5.7 million as part of a settlement over allegations it "illegally collected images, voice recordings, and geolocation" of children, some younger than 13.

The amount, part of an agreement with the Federal Trade Commission announced Wednesday, is the largest civil penalty ever issued by the agency in a child privacy case.

FTC commissioners Rohit Chopra and Rebecca Kelly Slaughter also filed a separate statement calling for TikTok executives to be held accountable in any future cases.

"In our view, these practices reflected the company's willingness to pursue growth even at the expense of endangering children," the statement read.

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The social media platform, known as Musical.ly when it was acquired by Chinese firm ByteDance in 2017, has a large following with preteens and teens and allows young users to post videos of themselves and contact other users through the app.

The FTC complaint, filed by the Department of Justice, accused the company of violating the Children's Online Privacy Protection Act, which requires social media platforms and websites to gain parental consent before collecting any data or information from users younger than 13.

The app https://t.co/g19LyIEi9Y, now known as @tiktok_us, illegally collected images, voice recordings, and geolocation of young children. The company will pay a record fine for violating the Children's Online Privacy Protection Act.https://t.co/7tohNYiW1c — Rohit Chopra (@chopraftc) February 27, 2019

FTC Chairman Joe Simons said in the agency's statement that TikTok operators knew a significant number of their users were younger than 13 and received thousands of complaints from parents.

"Even when parents contacted the company and asked that their child's personal information be deleted, the company failed to take adequate steps," Andrew Smith, director of the FTC's Bureau of Consumer Protection, said in a conference call Wednesday.

He said the company moved forward with deleting the users' accounts but did not delete their videos or content from its platform. In addition to the monetary penalty, the company must also comply with the child privacy law moving forward and remove all content made by children younger than 13.

"The concern is that kids don't know what's happening, and parents may or may not know its happening," Christine Elgersma, senior editor of parent education at Common Sense Media, an independent organization that reviews entertainment for families, told NBC News. "Few of us know what's happening with our data."

Users under the age limit will now only be allowed to like content and follow users and will be prohibited from creating or saving videos to the public TikTok network, according to TechCrunch.

Sen. Ed Markey, D-Mass., an author of the Children's Online Privacy Protection Act, responded to the FTC ruling, saying it "underscores what we have long known: companies do not consider children's personal information out of bounds."

"But the clock is ticking on companies that don't follow the law and protect the privacy of children."