Apple has reportedly removed Microsoft's Skype from the App Store in China on orders from the country's government.

"We have been notified by the Ministry of Public Security that a number of voice over internet protocol apps do not comply with local law," Apple told The New York Times on Tuesday. "Therefore these apps have been removed from the app store in China."

It's unclear what law Skype violated. The software is still available as an Android or Windows download on Microsoft's China site, which is operated by its local partner Guangming Founder. But at least six different Chinese app stores—which are listed by Guangming as places where Chinese users can download the tablet version of the Android Skype app—have also removed it.

Microsoft did not immediately respond for comment, but the company is reportedly working to reinstate Skype on the App Store.

Chinese internet users noticed Skype's disappearance on the App Store a month ago, and complained they could no longer buy Skype Credits, which can be used to make telephone calls. According to the Times, those who already downloaded Skype can still use it. But its removal from app stores may raise fears that the Chinese government will decide to eventually block Skype entirely.

Authorities there already block access to many foreign internet services including Twitter, Facebook, and Google's Gmail. The country's internet users instead rely on local Chinese-developed messaging apps that work with the government to block controversial content.

Foreign tech companies like Apple and Microsoft have been forced to comply with the tough internet restrictions in order to continue operating in the country. For instance, Apple earlier this year removed several virtual private network (VPN) services from its app store in China. These VPN services can essentially bypass China's online censorship and their removal prompted concern that Apple was bowing to pressure from the Chinese government at the cost of users' freedoms.