A Chinese regulator has reiterated that it suspects Microsoft has not fully disclosed issues related to the compatibility of its Windows OS and Office software suite, and has given the Redmond-based company 20 days to come up with a written explanation on the matter.

"Special investigation team conducted an anti-monopoly investigation inquiry with Microsoft Vice President Chen Shi (David Chen)", the State Administration for Industry and Commerce (SAIC), one of several agencies tasked with enforcing antitrust laws, said in a statement on its website.

The news comes around a month after SAIC raided Microsoft's offices in Beijing, Shanghai, Guangzhou, and Chengdu, taking possession of a couple of computers, emails, and other documents and internal correspondence. At that time, the agency said it was looking for information about how Windows and Microsoft Office are bundled, as well as about Windows-Office compatibility. The agency also revealed that it had received complaints from several companies regarding the security features of both.

Just last week, the agency confirmed that it is also probing the company over its Internet Explorer web browser and Windows Media Player. "Microsoft is suspected of incomplete disclosure of information related to Windows and Office software, as well as problems in distribution and sales of its media player and browser", Zhang Mao, the head of SAIC, had said.

Microsoft, which faced similar lawsuits in the US and EU, said it was "serious about complying with China's laws and committed to addressing SAIC's questions and concerns".

Aside from Microsoft, Qualcomm is also facing an anti-monopoly investigation in China. The US chipmaker is suspected of overcharging and abusing its market position in wireless communication standards.

China has increasingly sought to limit the use of US technology in the wake of Snowden's leaks. The Chinese authorities recently banned government use of Windows 8, and just last week there were reports that the Asian country is developing its own operating system.