China has largely blocked the WhatsApp messaging app, the latest move by Beijing to step up surveillance ahead of a big Communist Party gathering next month.

The disabling in mainland China of the Facebook-owned app is a setback for the social media giant, whose chief executive, Mark Zuckerberg, has been pushing to re-enter the Chinese market, and has been studying the Chinese language intensively. WhatsApp was the last of Facebook products to still be available in mainland China; the company’s main social media service has been blocked in China since 2009, and its Instagram image-sharing app is also unavailable.

The disruption of WhatsApp comes as Beijing prepares for the Communist Party’s congress, which starts Oct. 18.

By blocking the heavily encrypted WhatsApp service while making less secure applications like WeChat available to the public, the Chinese government has herded its internet users toward methods of communication that it can reliably monitor.

Full story: Keith Bradsher in The New York Times