US tech giant Microsoft said Sunday its offer to buy TikTok was rejected, as a deadline looms for the Chinese-owned video app to sell or shut down its US operations.

TikTok has been at the center of a diplomatic storm between Washington and Beijing, and President Donald Trump gave Americans a deadline to stop doing business with TikTok's Chinese parent company ByteDance -- effectively compelling a sale of the app to a US company.

Trump claims that TikTok could be used by China to track the locations of federal employees, build dossiers on people for blackmail and conduct corporate espionage.

"ByteDance let us know today they would not be selling TikTok's US operations to Microsoft," the US tech giant said in a statement referring to TikTok's owner.

"We are confident our proposal would have been good for TikTok's users, while protecting national security interests," the statement added.

Following Trump's executive order, Microsoft and Oracle were possible suitors to take over TikTok operations.

Microsoft said that it would have "made significant changes to ensure the service met the highest standards for security, privacy, online safety, and combatting disinformation."

TikTok has filed a lawsuit challenging the crackdown by the US government, contending that Trump's order was a misuse of the International Emergency Economic Powers Act because the platform is not "an unusual and extraordinary threat."

Downloaded 175 million times in the US, TikTok is used by as many as a billion people worldwide to make quirky, short-form videos on their cellphones. It has repeatedly denied sharing data with Beijing.