The Trump administration will ban WeChat and video-sharing app TikTok from U.S. app stores starting Sunday night, a move that will block Americans from downloading the Chinese-owned platforms over concerns they pose a national security threat.

The bans, announced on Friday, affect only new downloads and updates and are less sweeping than expected, particularly for TikTok, giving its parent group ByteDance some breathing space to clinch an agreement over the fate of its US operations.

WeChat, an all-in-one messaging, social media and electronic payment app, faces more severe restrictions from Sunday.

Existing TikTok users, on the other hand, will see...