TikTok stopped working for its 170 million American users late on Saturday before a law shutting it down on national security grounds took effect on Sunday, but a day before his inauguration, President-elect Donald Trump said "SAVE TIKTOK!

Millions of TikTok users in the United States are no longer able to watch videos on the social media platform as a federal ban on the immensely popular app takes effect.

Trump spoke to NBC News' Kristen Welker in an exclusive phone interview Saturday, discussing his plans on what to do about the popular social media app.