A Chinese competition regulator has given Microsoft 20 days to reply to queries on the compatibility of its Windows operating system and Office software suite amid a probe into the world's largest software company.

China's State Administration for Industry and Commerce questioned Microsoft Vice President David Chen and gave the company a deadline to make an explanation, the agency said.

Microsoft is one of at least 30 foreign companies that have come under scrutiny by China's anti-monopoly regulators as the government seeks to enforce its six-year old competition law. 

Critics say the law is being used to unfairly target overseas businesses, a charge the regulators deny. 

According to a state media report, Microsoft's use of verification codes also spurred complaints from Chinese companies. 

Their use "may have violated China's anti-monopoly law", the official Xinhua news agency said today. 

Verification codes are typically used by software companies as an anti-piracy mechanism. They are provided with legitimate copies of software and can be entered to entitle customers to updates and support from the manufacturer. 

Microsoft has long suffered from piracy of its software within China. 

Former CEO Steve Ballmer told employees in Beijing that the company made less revenue in China than it did in the Netherlands. 

Last month, a delegation from chipmaker Qualcomm, led by company President Derek Aberle, met officials at the National Development and Reform Commission (NDRC) as part of that regulator's investigation of the San Diego-based firm. 

NDRC said earlier this year that the US chipmaker is suspected of overcharging and abusing its market position in wireless communication standards. 

Microsoft CEO Nadella is expected to make his first visit to China as chief executive later this month.