TikTok chief executive Kevin Mayer has quit the video-sharing app ahead of an impending ban by US President Donald Trump.
The Chinese-owned firm has been accused of being a threat to US national security by the Trump administration.
Mr Mayer joined TikTok in June after leaving his role as Disney's head of streaming services.
TikTok was given 90 days to be sold to an American firm or face a ban in the US.
"In recent weeks, as the political environment has sharply changed, I have done significant reflection on what the corporate structural changes will require, and what it means for the global role I signed up for," Mr Mayer said in a letter to employees.
"Against this backdrop, and as we expect to reach a resolution very soon, it is with a heavy heart that I wanted to let you all know that I have decided to leave the company," Mr Mayer added.
Both TikTok and Chinese messaging app WeChat face bans in the US as tensions rise between Washington and Beijing over a wide range of issues including national security concerns about Chinese tech firms.
"We appreciate that the political dynamics of the last few months have significantly changed what the scope of Kevin's role would be going forward, and fully respect his decision. We thank him for his time at the company and wish him well," a spokesman for TikTok said.
President Trump's executive order prohibits transactions with TikTok's owner ByteDance from mid-September. The firm has gone to court to challenge the ban.
Officials in Washington are concerned that TikTok could pass American users' data to the Chinese government, something ByteDance has denied doing.
Tiktok said the Trump administration's move was motivated by politics, not national security.
US tech giant Microsoft has confirmed that it is continuing talks to purchase the US operations of TikTok.
BDST: 1232 HRS, AUG 27, 2020