Kevin Mayer, CEO of TikTok, resigned on Thursday amid U.S. pressure for its Chinese owner to sell the popular video app, which the White House says is a security risk.

The parent company of TikTok, a Chinese video-sharing app, has announced it is taking legal action against the US government, in an effort to safeguard its rights and interests.

Microsoft said Microsoft and Chinese company ByteDance have provided notice of their intent to explore a deal resulting in Microsoft owning and operating the TikTok service in the U.S., Canada, Australia and New Zealand.