WASHINGTON (Reuters) -TikTok's fortunes took a positive turn on Thursday as a growing number of U.S. officials said its Chinese owner should have more time to sell the app and stop it from being banned ahead of President-elect Donald Trump's return to the White House.

Trump's incoming national security adviser said the new Republican administration will keep the social media app used by 170 million Americans alive in the U.S. if there is a viable deal and top Senate Democrat Chuck Schumer urged President Joe Biden to extend by 90 days a deadline to shut it down on Sunday.

A law passed in April mandates TikTok's owner, ByteDance, divest TikTok's U.S. assets by Sunday to a non-Chinese buyer, or be banned on national security concerns.

"We will put measures in place to keep TikTok from going dark," U.S. Representative Mike Waltz told Fox News, pointing to a provision in the law allowing for a 90-day extension if there is "significant progress" toward a divestiture.

"Essentially that buys President Trump time to keep TikTok going," said Waltz, who was picked by Trump to be his national security adviser.

A White House official said on Thursday the Biden administration does not plan to enforce the ban on Sunday leaving it up to the Trump administration, though it is not clear if the app will remain online absent a formal extension.

"Given the timing of when it goes into effect over a holiday weekend a day before inauguration, it will be up to the next administration to implement," the official said.

The U.S. Supreme Court is currently deciding whether to uphold the law and allow TikTok to be banned on Sunday absent a divestiture, overturn the law or pause it to give the justices more time to make a decision.

The court said it may issue rulings on Friday, but as is customary, did not state which case or cases would be decided.

Trump once supported a ban on the app but changed his stance last year. His shift came amid growing signs of support for his presidential campaign among tech executives and overtures from Republican donor Jeff Yass, who owns a big share of ByteDance.

In a sign of warming ties between Trump and TikTok, the video app's CEO, Shou Zi Chew, will attend the presidential inauguration on Jan. 20 and be seated on the dais among other high-profile invitees, two people familiar with the matter told Reuters.

BIPARTISAN SHIFT

"It's clear that more time is needed to find an American buyer and not disrupt the lives and livelihoods of millions of Americans," Schumer said on the Senate floor, adding that Democrats tried to pass a bill extending the deadline to find a solution to 270 days.

"I will work with the Trump administration and with both parties to keep TikTok alive while protecting our national security," he added.

The comments by Schumer, who was a strong supporter of the law to force a sale, are a sign of the growing concern among prominent Democrats about the potential impact and political fallout of shutting down TikTok.

The New York Times reported Trump is considering an executive order that would seek to allow TikTok to continue operating despite a pending legal ban until new owners are found. It was not immediately clear if Trump has the authority to do so given the legal divestiture requirements imposed by Congress.

TikTok did not respond to requests for comment.

A spokeswoman for the Trump transition, Karoline Leavitt, said, "President Trump has repeatedly expressed his desire to save TikTok, and there's no better deal maker than Donald Trump."

'TALKS A BIG GAME'

Still, several Republicans and Democrats remain concerned about Chinese ownership of the app, worried the Chinese government could use it as a tool to collect data on U.S. citizens and to spread propaganda to the public.

"Trump talks a big game on China & wanted to ban TikTok - just like many Republicans voted to do," Representative Frank Pallone, the top Democrat on the Energy and Commerce Committee, wrote on the social media platform X.

"But now he's inviting TikTok's CEO to sit beside him at his inauguration even though TikTok is linked to the CCP & is a threat to our national security. What message does this send?"

The prospect of a TikTok ban has already triggered some users to seek alternatives, with Chinese social media app RedNote gaining nearly 3 million U.S. users in one day earlier this week, according to analytics firm Similarweb.

Reuters reported that TikTok plans to shut U.S. operations of its social media app on Sunday barring a last-minute reprieve, according to people familiar with the matter.

Privately held ByteDance is about 60% owned by institutional investors such as BlackRock and General Atlantic, while its founders and employees own 20% each. It has more than 7,000 employees in the United States.