TikTok is being investigated by the US Justice Department for spying on its citizens and journalists, it is reported.
The Chinese company is owned by ByteDance, who are based in Beijing, and reportedly has close ties with the Chinese government.
Reports say the FBI, lawyers for the Eastern District of Virginia and the US Justice Department are investigating ByteDance after the short-form video platform admitted in December to harvesting data from American citizens and two of its journalists.
The company has refused to comment on the allegations.
The reported investigation comes after the White House pursued a tougher stance on the Chinese company amid fears over national security.
Officials fear China could be using the hugely popular app to acquire data and spy on Americans as well as looking to undermine democratic institutions.
TikTok revealed earlier this week Joe Biden had demanded its owner to put the company up for sale after it was blocked form government mobile phones in the US and Europe.
Some of the ByteDance employees, who were fired by the company, had reportedly been attempting to find the sources of leaks and business documents to journalists.
According to the New York Times, the workers gained access to the IP addresses of the reporters and the people they were connected to on the app.
It was revealed two of the employees were based in China and had been trying to obtain sensitive data.
However, the company tried to play down the alleged breaches and said it would try and prevent breaches in the future.
TikTok's attempt to assure the US government has not gone down well with politicians on both sides who want to block or ban the app.
Mr Biden has said he would consider the attempt to ban the app in the US - with the proposal making its way through Congress.
Relations between China and the US have deteriorated in the last year despite TikTok officials trying to lobby the White House administration.
Maureen Shanahan, a spokesperson for TikTok, said selling the company would not solve the problem of security fears.
She said in a statement last week: "If protecting national security is the objective, divestment doesn’t solve the problem: A change in ownership would not impose any new restrictions on data flows or access."
Wang Wenbin, from the Chinese foreign ministry, has hit out at the US and said it should stop spreading "disinformation about data security."
He said: "The US should stop spreading disinformation about data security, stop suppressing the relevant company, and provide an open, fair and non-discriminatory environment for foreign businesses to invest and operate in the US."
TikTok, which has more than 100 million US users, has also come under-fire from Canada who said the company posed an "unacceptable risk" and banned the app on government devices.
It follows the EU who have blocked the app along with Taiwan, Afghanistan and India.
