The Chinese government has disabled Facebook-owned messaging service WhatsApp, the New York Times reports.

Nadim Kobeissi, an applied cryptographer at Paris-based research firm Symbolic Software, told the Times his company began noticing slowdowns in the service Wednesday. By Monday, the block had become comprehensive.

Authorities blocked video-chat and file-sharing functions within WhatsApp in mid-July, but the app’s messaging capabilities, which employ a rare and strong form of encryption, remained functional. The government lifted bans on video chat and file sharing later, but has since disabled the app in its entirety, reports say.

WhatsApp’s messaging service uses a renowned end-to-end encryption technique. As the Times explains it, even Facebook itself cannot decode messages sent via the app. The encryption method is not widely used and is therefore difficult to compromise.

But the ban, as the Times points out, indicates that Chinese authorities have developed a means by which to breach WhatsApp messaging encryption.

“This is not the typical technical method in which the Chinese government censors something,” Kobeissi said.

Censorship of various technological communication services is commonplace in the country. If the government does not disable a service entirely, it slows down that service to such a degree that it becomes unusable.

“If you’re only allowed to drive one mile per hour, you’re not going to drive on that road, even if it’s not technically blocked,” Lokman Tsui, an internet communications specialist at the Chinese University of Hong Kong, explained to the Times.

The goal of the censorship is to funnel users toward a handful of communication services that the government can easily monitor. WeChat is one such service. It is similar to WhatsApp except that the former, according to the Times, offers broader functionality.

Tencent, the company that runs WeChat, is based in Shenzhen and has said that it will comply with the government’s requests for information. In total, 963 million people use WeChat, the Times says.

Services like WhatsApp and WeChat have largely replaced e-mail in China, and are vital to many business operations. A large number of China-based businesses were unwilling to use WeChat, whether because of the threat of surveillance or some other reason.

Some former WhatsApp users in China expressed frustration on social media, the Times reports.

“Losing contact with my clients, forced back to the age of telephone and email for work now,” one user complained on Weibo, a Twitter-like microblogging site.

“Even WhatsApp is blocked now? I’m going to be out of business soon,” another person said via the same site.

WhatsApp was the last Facebook product available in mainland China, the Times says. The country banned the company’s main social media site in 2009. Instagram, another Facebook offering, is disabled as well.

The WhatsApp ban represents a setback for the social media behemoth, whose founder and chief executive, Mark Zuckerberg, has been advocating and taking steps toward re-entering the Chinese market.

The handful of American-created communication services China does tolerate include Microsoft’s Skype and Apple’s FaceTime. The former does not employ end-to-end encryption, the Times points out, and is, therefore, easier for the government to monitor. The latter does use end-to-end encryption but is less secure than WhatsApp.

The Times notes that the Office of the United States Trade Representative is investigating whether Chinese authorities have violated the intellectual property rights of American citizens. The Office has not clarified whether it will consider the bans as part of the investigation, or merely look for cases in which China has stolen US technology.

The WhatsApp ban comes just prior to the country’s Communist Party Congress on October 18, during which authorities appoint the leaders of the party, who in turn run the country.

According to the Times, the meeting, which the country holds once every five years, will likely reinstall President Xi Jinping as party leader. The question remains as to who will join Xi on the Standing Committee of Politburo, the party’s highest ranking group.

Under Xi’s leadership, the Times notes, China has tightened censorship, closed several churches and jailed a number of human rights activists.

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