President Donald Trump has repeatedly insisted that any sale of TikTok's US operations would have to include a substantial payment to the United States - but it was not clear under what authority he can extract a payout.

Earlier on Monday, Mr Trump said TikTok will have to close in the US by Sept 15 - unless there is a deal to sell the social network's domestic operations to Microsoft or another US company.

Mr Zhang Yiming, the founder of ByteDance, which owns TikTok, said the US government did not aim to force the sale of TikTok, but rather wanted to ban it. While a forced sale of TikTok to a US buyer is "unreasonable", the company has no choice but to abide by the law, he said.

Beijing has leapt to TikTok's defence, accusing the US of "outright bullying".

SEE WORLD: Washington determined to ban TikTok, no matter what, says owner ByteDance