WASHINGTON, Mar. 11 (Reuters) - U.S. presidential candidate Donald Trump said on Monday TikTok was a national security threat but also said a ban on the popular app would hurt some kids and only strengthen Meta Platforms' (META.O), opens new tab Facebook, which the Republican has harshly criticized.

Trump reiterated his concerns as lawmakers weigh a bill this week that would give TikTok's Chinese owner ByteDance about six months to divest the short video app used by 170 million Americans.

The U.S. House of Representatives is set to vote on Wednesday under fast-track rules that require two-thirds of members to vote "yes" for the measure to win passage.

TikTok told Congress late Monday in a letter seen by Reuters it is "not owned or controlled by the Chinese government" and argued if the company was sold another buyer would not continue TikTok's $1.5 billion effort to protect U.S. data.

"Ironically, U.S. user data could be less secure under a divestment scheme," the company said.

The FBI, Justice Department and Office of the Director of National Intelligence plan to hold on Tuesday a classified briefing for House members, two sources said. FBI Director Chris Wray reiterated concerns about TikTok at a hearing on Monday.

The 2024 Annual Threat Assessment of the U.S. Intelligence Community released on Monday said "TikTok accounts run by a PRC propaganda arm reportedly targeted candidates from both political parties during the U.S. midterm election cycle in 2022."

The Justice Department detailed its security concerns about TikTok in a document last week first reported by Reuters.

"I'm not looking to make Facebook double the size," Trump told CNBC on Monday. "And if you if you ban TikTok, (then) Facebook and others, but mostly Facebook, will be a big beneficiary. And I think Facebook has been very dishonest."

Trump met recently with investor Jeff Yass, whose investment firm Susquehanna International Group has a stake in ByteDance, he confirmed on CNBC. Trump said they did not talk about TikTok.

Meta Platforms shares closed down 4.4% at $483.59 on Monday. The company declined to comment.

Photo from Reuters