WASHINGTON — President Donald Trump repeatedly insisted on Monday that the government should get a cut from the sale of TikTok's US unit if an American firm buys it but it wasn’t clear under what authority he can extract a payout.

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.

“The United States should get a very large percentage of that price because we’re making it possible,” Trump said at a news conference on Monday evening. “Whatever the number is, it would come from the sale, which nobody else would be thinking out but me, but that’s the way I think. And I think it’s very fair.”

Earlier in the day, Trump also warned he will ban the app, which is owned by China's ByteDance, on Sept. 15 if there is no deal.

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

The Trump administration has accused TikTok and others of providing data to the Chinese government, which Beijing and TikTok deny.

It would be unprecedented, based on recent history, for the US government to collect a cut of a transaction involving companies in which it doesn’t hold a stake. Trump said the money would come from China or an American buyer such as Microsoft Corp.

The request for payment to the US Treasury further complicated negotiations as legal experts highlighted that such a demand to secure regulatory approval for a takeover deal would be highly unorthodox.

However, Trump compared the arrangement to landlord-tenant dynamics. “Without the lease, the tenant doesn’t have the value,” he said. “Well, we’re sort of in a certain way the lease. We make it possible to have this great success.”

Meanwhile, the state-run China Daily newspaper said on Tuesday that Beijing would not accept the "theft" of a Chinese technology company.

It also warned in an editorial that China had "plenty of ways to respond if the administration carries out its planned smash and grab". — Agencies