TikTok went dark for American users in an unprecedented display of the U.S.-China divide over technology and national security.The app started halting service Saturday night for 170 million users in its most important market shortly before a law took effect requiring it to shed its Chinese ownership or close in the U.

The Chinese-owned company said it would cut off its services unless the U.S. assures Apple, Google and other companies that they would not be punished for hosting and distributing TikTok.