July 26 (Reuters) - The U.S. Department of Justice asked

a federal appeals court late on Friday to uphold an April law

requiring China-based ByteDance to sell TikTok's U.S. assets by

Jan. 19 or face a ban.

The DOJ argued in its filing that TikTok under Chinese

ownership poses a serious national security threat because of

its access to vast personal data of Americans, asserting China

can covertly manipulate information that Americans consume via

TikTok.

"The serious national-security threat posed by TikTok is

real," the department said. "TikTok provides the Chinese

government the means to undermine U.S. national security in two

principal ways: data collection and covert content

manipulation."

The Biden administration asked the U.S. Court of Appeals for

the District of Columbia to reject lawsuits by TikTok, parent

company ByteDance and a group of TikTok creators seeking to

block the law that could ban the app used by 170 million

Americans.

TikTok has repeatedly denied it would ever share U.S. user

data with China or that it manipulates video results.

"The government has never put forth proof of its claims,

including when Congress passed this unconstitutional law. Today,

once again, the government is taking this unprecedented step

while hiding behind secret information", TikTok posted on social

media platform X in response to the DOJ brief.

The DOJ's filing details wide-ranging national security

concerns about ByteDance's ownership of TikTok.

"China's long-term geopolitical strategy involves developing

and pre-positioning assets that it can deploy at opportune

moments," the department said.

The government acknowledged in a separate declaration it had

no information that the Chinese government had gained access to

the data of U.S. TikTok users but said the risk of the

possibility was too great.

"The United States is not required to wait until its foreign

adversary takes specific detrimental actions before responding

to such a threat," the filing said.

PRESIDENTIAL ELECTION ISSUE

The government also filed a classified document with the

court detailing additional security concerns about ByteDance's

ownership of TikTok, as well as broader declarations from the

FBI, Office of the Director of National Intelligence and DOJ's

National Security Division.

ByteDance told the U.S. government that TikTok's source code

contained 2 billion lines of code making a full review

impossible. "Oracle estimated it would require three years to

review this body of code," excluding additional changes, DOJ

added.

Signed by President Joe Biden on April 24, the law gives

ByteDance until Jan. 19 to sell TikTok or face a ban. The White

House says it wants to see Chinese-based ownership ended on

national security grounds, but not a ban on TikTok.

The department rejected all the arguments raised by TikTok,

including that the law violates the First Amendment free speech

rights of Americans who use the short video app, saying the law

addresses national security concerns, not speech, and is aimed

at China's ability to exploit TikTok to access Americans'

sensitive personal information.

TikTok users have "numerous other well-known platforms" such

as YouTube, Facebook, Instagram, Snapchat and X that they could

use instead, the DOJ said.

The DOJ added TikTok's $2 billion plan to protect U.S. user

data was insufficient, saying the company's proposed agreement

was not enough in part because U.S officials do not trust

ByteDance and in the government's "lack of confidence that it

had either the resources or capability to catch violations."

The appeals court will hold oral arguments on the legal

challenge on Sept. 16, putting the issue of TikTok's fate into

the final weeks of the Nov. 5 presidential election.

Republican presidential nominee Donald Trump has joined

TikTok and said in June he would never support a TikTok ban.

Vice President Kamala Harris, who is poised to become the

Democratic nominee, joined TikTok this week.

The law prohibits app stores like Apple ( AAPL ) and

Alphabet's Google from offering TikTok and bars

internet hosting services from supporting TikTok unless it is

divested by ByteDance.

Driven by worries among U.S. lawmakers that China could

access data on Americans or spy on them with the app, Congress

overwhelmingly passed the measure just weeks after it was

introduced.