The person said that when she called the police, she was told that the service suspensions were aimed at people who had not linked their identification to their account; used virtual private networks, or V.P.N.s, to evade China’s system of Internet filters, known as the Great Firewall; or downloaded foreign messaging software, like WhatsApp or Telegram.

With debates continuing in Europe and the United States about how heavily to encrypt communications sent through smartphone messaging applications that could mask terrorist plots from law enforcement, the move in China underlines Beijing’s determination to control and monitor information online. The debate in the West also has influence in China, said Nicholas Bequelin, the East Asia director for Amnesty International in Hong Kong.

“With the West generally going backward in terms of protecting privacy and freedom of expression, China is comforted in its longstanding position that it is the arbiter of what can be said or not,” he said.

The action also shows that despite spending billions of dollars to create one of the world’s most sophisticated Internet censorship and surveillance systems, blind spots abound. The Chinese government has long focused on software that circumvents the Great Firewall, like virtual private networks. But the move to suspend mobile phone accounts linked to the software demonstrates a new level of urgency.

Beijing has at times bolstered its filters against virtual private networks, and has been taking increasingly aggressive steps over the last year to censor Internet content. In March, China turned the Great Firewall into a powerful weapon that redirected incoming traffic to sites abroad that it deemed hostile. The campaign for tighter Internet control is led by Lu Wei, China’s Internet czar since 2013, who has been reining in social media and has implored foreign tech leaders and policy makers to show “respect of national sovereignty” on the Internet.