"We regret that a US law banning TikTok will take effect on January 19 and force us to make our services temporarily unavailable," read a notification to US users who opened the app Saturday night.

"We're working to restore our service in the US as soon as possible, and we appreciate your support. Please stay tuned," the message added.

After months of legal tussles, the US Supreme Court on Friday upheld a law that would ban the popular video-sharing platform in the name of national security, unless its Chinese owners reach a deal to sell it to non-Chinese buyers by Sunday.

Only months after overwhelmingly backing the law, lawmakers and officials were now fretting about the ban, with all eyes on whether Trump can swoop in and find a way to save the app.

From teenage dancers to grandmothers sharing cooking tips, TikTok has been embraced for its ability to transform ordinary users into global celebrities when a video goes viral.

It also has a fan in Trump, who has credited the app with connecting him to younger voters, contributing to his election victory in November.

After discussing TikTok with Chinese President Xi Jinping, Trump told NBC News on Saturday that he could activate a 90-day reprieve after he reclaims the Oval Office.

"I think that would be, certainly, an option that we look at. The 90-day extension is something that will be most likely done, because it's appropriate," he said, ahead of Monday's inauguration.

"If I decide to do that, I'll probably announce it on Monday."

The law allows a 90-day delay if the White House can show progress toward a viable deal, but TikTok owner ByteDance has flatly refused any sale.

The administration of outgoing President Joe Biden has said it will leave the matter to Trump, and White House spokeswoman Karine Jean-Pierre qualified TikTok's latest statements as a "stunt."

After the court defeat, TikTok CEO Shou Chew appealed to Trump, thanking him for his "commitment to work with us to find a solution."

Trump "truly understands our platform," he added.

TikTok has been lobbying furiously to thwart the law's implementation, with Chew set to attend Trump's inauguration on Monday.

The law requires Apple and Google to remove TikTok from their app stores, blocking new downloads. The companies could face penalties of up to $5,000 per user who can access the app.

Oracle, which hosts TikTok's servers, would also be legally obligated to enforce the ban.

None of the companies responded to requests for comment on Saturday.

- Offers for TikTok -

A last-minute proposal made Saturday by the highly-valued start-up Perplexity AI offered a merger with the US subsidiary of TikTok, a source with knowledge of the deal told AFP.

That deal could allow parent company ByteDance a possible solution without selling off the app entirely.

The plan, first reported by US broadcaster CNBC, would create a new joint venture combining the assets of US TikTok and Perplexity AI, which has been backed by Amazon founder Jeff Bezos.

The proposal did not include a price for the transaction, but the source estimated it would be at least $50 billion.

Frank McCourt, the former Los Angeles Dodgers owner, has also made an offer to purchase TikTok's US activity and said he's "ready to work with the company and President Trump to complete a deal."

Canadian investor Kevin O'Leary, who is involved in that offer, told Fox News that ByteDance was offered $20 billion for TikTok's US operation.

He acknowledged the legal uncertainty over the case, with it remaining an open question whether an executive order by Trump to halt the ban would override the law.

"Congress wrote this law to be virtually president-proof," warned Adam Kovacevich, chief executive of industry trade group Chamber of Progress.

Sarah Kreps, a professor of government and law at Cornell University, said that "if an executive order conflicts with an existing law, the law takes precedence, and the order can be struck down by the courts."

If TikTok is forced into a shutdown, its US-based rivals Instagram Reels and YouTube Shorts would benefit.

Thousands of worried TikTok users have protectively turned to Xiaohongshu ("Little Red Book"), a Chinese social media network similar to Instagram.

Nicknamed "Red Note" by its American users, it was the most downloaded app on the US Apple Store this week.

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