The UK's data protection watchdog on Monday announced investigations into three social media networks, including TikTok and Reddit, over their use of children's personal data.

Growing concerns that young people could be sent inappropriate or harmful content from social media apps prompted the probes, the Information Commissioner's Office (ICO) said in a statement.

"The responsibility to keep children safe online lies firmly at the door of the companies offering these services and my office is steadfast in its commitment to hold them to account," said Information Commissioner John Edwards.

The ICO will look into how Chinese-owned TikTok uses the personal information of 13-to-17-year-olds to make recommendations and deliver content to their social media feeds.

Online forum site Reddit and image-sharing site Imgur are under investigation over their age assurance measures as well as personal information use.

"We're deeply committed to ensuring a positive experience for young people on TikTok," a company spokesperson said in a statement to AFP.

TikTok has "comprehensive measures that protect the privacy and safety of teens, including industry-leading safety features and robust restrictions on the content allowed in teens' feeds", the firm added.

The other two platforms had yet to respond.

In 2023, the ICO fined popular video-sharing app TikTok several million pounds for failing to obtain consent of parents or guardians to use children's data, after they had set up accounts despite being too young.