President Donald Trump said Monday the U.S. government should get a "substantial portion" of the sales price of the U.S. operations of popular short-video app TikTok and warned he will ban the service in the United States on Sept. 15 without a sale.

The turnaround came after Trump on Friday said he was planning to ban the Chinese-owned video app's U.S. operations as soon as Saturday after dismissing a possible sale to Microsoft.

Reuters reported last week that some investors are valuing TikTok at about $50 billion, citing people familiar with the matter.

Donald Trump says the government should get a cut from the sale of TikTok's US unit if an American firm buys it.

The US president said he made a demand for a "substantial portion" of the purchase price in a phone call at the weekend with Microsoft's boss.

He also warned he will ban the app, which is owned by China's ByteDance, on 15 September if there is no deal.

ByteDance is under pressure to sell its US business after Mr Trump threatened a crackdown on Chinese tech companies.

The president’s interventions in company dealings based on his own instincts are a departure from the arm’s-length approach of predecessors of either party.

President Trump campaigned on a promise to run the economy like his business empire. And for almost four years, he has unabashedly wielded the power of the presidency to insert himself into corporate affairs, helping some companies and punishing others in line with his instincts and inclinations.