Microsoft Corp.'s China unit said Wednesday it has always abided by laws and regulations in China and will "actively answer" questions raised in an anti-monopoly case.

Microsoft China's statement came one day after the market regulator confirmed an investigation into Microsoft.

Microsoft claims to have a monitoring and implementation mechanism to ensure compliance of its operations in different markets and there is no exception for the Chinese market.

The State Administration for Industry & Commerce (SAIC) confirmed on Tuesday it had visited Microsoft China Co., Ltd, and three of its branches in Shanghai, Guangzhou and Chengdu.

SAIC said Microsoft had not fully disclosed anti-competition information about its Windows operating system and Microsoft Office application as required.

Inspectors are investigating a vice president and senior managers, and have made copies of the firm's financial statements and contracts.

The administration has seized documents, e-mails and other data from computers and servers. It has not been able to complete its investigation because key personnel are not in China or cannot be contacted.

In June last year, the SAIC investigated complaints from enterprises that Microsoft had used tie-in sales and verification codes in Windows and Microsoft Office that caused software incompatibility issues.

Microsoft failed to fully disclose information as required by the SAIC about such complaints in its reports submitted to the regulator, and may have breached China's Anti-Monopoly Law, the statement said.

Under the law, companies or individuals should not abuse their market dominance to exclude or restrict competition and should be supervised by the public.