The Chinese government is restricting access to WhatsApp’s full suite of services in the country, a security expert confirmed.

Following short-term disruptions to WhatsApp voice and video chats, and the sending of images from the app starting in July, the popular service’s text messages are now being blocked, The New York Times (NYT) reported.

According to Nadim Kobeissi, an applied cryptographer at Symbolic Software, the broad disruption of WhatsApp in China suggests the country’s censors have developed specialised software to block the messages, which rely on encryption technology used by few services other than WhatsApp, NYT reported.

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

The software and applied cryptography consulting company also monitors digital censorship in China.

China’s government is stepping up its campaign of censorship ahead of the Communist Party congress in mid-October. President Xi Jinping took power at the last congress in 2012.

WhatsApp is owed by Facebook, which was blocked in China in 2009. Facebook’s Instagram app is also blocked.

Meanwhile, the Cyberspace Administration of China this week fined three social media companies – Baidu, Tencent and Weibo – for failing to properly censor content on their platforms.

In July the government started shutting down China-based VPN providers and targeting overseas services as it tightens control over the internet, following new regulations to crack down on services which bypass the country’s massive firewall to access overseas sites.The government passed laws in January banning all VPNs not approved by state regulators.

Apple agreed to remove “some” VPN applications from the App Store in China.