WASHINGTON (CN) — Meta CEO Mark Zuckerberg wrapped his 13-hour stint on the witness stand Wednesday in a landmark antitrust trial over his purchase of Instagram and WhatsApp in the early 2010s, during which he argued that Meta still faces steep competition from YouTube and TikTok.

Meta CEO Mark Zuckerberg emphasized Wednesday that his social media company faces stiff competition from TikTok, as Meta seeks to fend off accusations from the Federal Trade Commission (FTC) that it has a monopoly over social networking.

Mark Zuckerberg said that ByteDance Ltd.’s TikTok posed a “highly urgent” competitive threat to Meta Platforms Inc. when it first sprang up in 2018, as he testified for a third day in the Federal Trade Commission’s antitrust trial.