WASHINGTON (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' 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.

'KIDS WILL GO CRAZY'

Trump previously criticized the company now called Meta Platforms for revoking his access to Facebook and Instagram after removing two of his posts during the Jan. 6, 2021, U.S. Capitol riot. His accounts were reinstated in February 2023.

Trump also said a TikTok ban could impact young people. "There are a lot of young kids on TikTok who will go crazy without it," he said. "There's a lot of good and there's a lot of bad with TikTok."

Tiktok CEO Shou Zi Chew will visit Capitol Hill later this week on a previously scheduled trip to talk to senators, a source briefed on the matter said.

President Joe Biden said last week he would sign the bill after a committee unanimously approved the measure.

TikTok, which says it has not and would not share U.S. user data with the Chinese government, argues the House bill amounts to a ban. It is unclear if China would approve any sale or if TikTok could be divested in six months.

House Majority Leader Steve Scalise said "we must ensure the Chinese government cannot weaponize TikTok against American users and our government through data collection and propaganda."

The bill would give ByteDance 165 days to divest TikTok. If it failed to do so, app stores operated by Apple, Alphabet's Google and others could not legally offer TikTok or provide Web hosting services to ByteDance-controlled applications.

In 2020, Trump sought to ban TikTok and Chinese-owned WeChat but was blocked by the courts.

The app is popular and getting legislation approved by both the House and Senate in an election year may be difficult. Last month, Biden's re-election campaign joined TikTok.

Trump's campaign has not joined TikTok.

(Reporting by Susan Heavey and David Shepardson in Washington; Editing by Bernadette Baum, Franklin Paul, Matthew Lewis and Lincoln Feast.)