Skype has apparently joined the lengthening list of Internet communication tools on China’s blacklist, with Apple saying Wednesday it was ordered to clear its download store of apps that violate national laws. Skype is no longer available for download on the China Apple Store or Android sites, with Chinese web-users saying it had been gone for weeks.

“We have been notified by the Ministry of Public Security that a number of VoIP (voice over Internet protocol) apps do not comply with local law, therefore these apps have been removed from the App Store in China,” Apple said in an emailed statement.

“These apps remain available in all other markets where they do business.”

The company did not specify which laws such apps were found to have violated.

But China has tightened its already stringent online policing this year, including enacting new rules that require tech companies to store user data inside the country as well as imposing new restrictions on what is permissible content.

Chinese authorities appeared to severely disrupt the WhatsApp messaging app as they ratcheted up security ahead of a Communist Party congress in October that saw President Xi Jinping consolidate his hold on the country.

The moves have prompted speculation on the Chinese Internet that authorities were moving against services with effective encryption, like WhatsApp and Skype, that make them less vulnerable to government monitoring.

Skype Business, a separate app tailored more for corporate use, was still available for download.

China has for years blocked leading foreign websites or services including Facebook, Twitter, Instagram and a number of news organizations with a system of Internet censorship nicknamed the “Great Firewall of China.”

Skype’s removal from app stores comes as China prepares to host its fourth World Internet Conference next month.

The annual event in eastern China is used by Beijing to promote its views about web policy, but has been criticized by rights groups.

On Tuesday the ruling Communist Party’s anti-graft agency said China’s former Internet czar Lu Wei, who stepped down last year after overseeing a tightening of online censorship, was under investigation for suspected “severe disciplinary violations,” which typically means corruption.