The world’s most popular messaging app WhatsApp has been blocked in China. It comes as the latest move by the Chinese Government to broaden censorship ahead of its Communist Party meeting next month. According to a report in the New York Times, WhatsApp has been “broadly disrupted in China.”

WhatsApp has been partially blocked over the last few months in China. Users were not able to send videos or photos. But on Monday, China seems to have upgraded its firewall and users are not able to send text messages, too.

WhatsApp was the last of Facebook products to still be available in mainland China. The company’s main social media site has already been blocked in China since 2009, and its image-sharing app Instagram is also not available there since 2014.

The reason behind this blocking could be the difficulty to put the WhatsApp chats on surveillance. Since, the messaging app provides the end-to-end encryption, which means that even Facebook does not know what is being said in the conversations passing through its servers. This could have drawn the attention of Chinese censors.

The blocking of WhatsApp text messages suggests that China’s censors may have developed specialized software to interfere with such messages, which rely on an encryption technology that is used by few services other than WhatsApp,’’ a Paris-based cryptographer told NY Times.

With WhatsApp being blocked completely, WhatsApp users in China may have to switch to WeChat, a popular messaging service in the country. WeChat is owned by a Chinese internet company- Tencent, that recently revealed that it submits all its data, including private user data, to the Chinese government.

The Chinese government has a long history of mostly blocking or limiting access to internet services, especially social networks. Apart from Facebook and its products, Wikipedia, Twitter, and many Google services are also currently blocked in mainland China.