Microsoft Corp denied on Wednesday it was omitting websites from its Bing search engine results for users outside China after a Chinese rights group said the U.S. firm was censoring material the government deems politically sensitive.

GreatFire.org, a China-based freedom of speech advocacy group, said in a statement on Tuesday that Bing was filtering out both English and Chinese language search results for terms such as "Dalai Lama", the exiled Tibetan spiritual leader whom Beijing brands as a violence-seeking separatist, charges he denies.

Microsoft, responding to the rights group's allegations, said a system fault had removed some search results for users outside China. The company has in the past come under fire for censoring the Chinese version of internet phone and messaging software Skype.

"Due to an error in our system, we triggered an incorrect results removal notification for some searches noted in the report but the results themselves are and were unaltered outside of China," Stefan Weitz, senior director for Bing, said in a statement emailed to Reuters on Wednesday.

Weitz did not say if the error had been fixed and Microsoft officials in Beijing declined to elaborate.

Microsoft sent a shortened version of the statement to China-based media organizations which omitted all reference to GreatFire.org and did not address the allegations.

"There were too many points in the original statement," a China-based Microsoft spokeswoman told Reuters.

Reuters reporters found that Bing omitted several websites that showed up on the search engine of rival Google Inc when they searched for "Dalai Lama" in Chinese from Singapore. The English-language search results on both engines were similar.

China's ruling Communist Party sees censorship as key to maintaining its grip on power, recognizing that social media offers a platform for citizens to air grievances and criticism of the government, a potential trigger for social unrest.

This censorship often means foreign Internet companies must tread a careful path in China to exploit business opportunities without compromising a carefully nurtured image as champions of open societies and free speech.

All internet firms operating in China comply with the government's web censorship requirements.

Microsoft has made no secret of its aim to build a bigger presence in China, a market where its software is widely used but rarely paid for.

Microsoft was criticized for censoring the Chinese version of Skype, which it ran jointly with Hong Kong-based TOM Group. In November, Microsoft said it had formed a new joint venture with Guangming Founder, and advocacy group GreatFire.org said Skype in China was no longer being censored.