A senior official in Chongqing municipality in Southwest China was removed from his post on Friday after the local disciplinary watchdog confirmed he had appeared in a widespread online sex video.

Lei Zhengfu, Party secretary of Chongqing's Beibei district, has been sacked and is under investigation, according to a statement from the information office of the Chongqing government released on Friday.

Lei joins officials who have been sacked after negative pictures or tapes were posted on the social network Sina Weibo, a Twitter-like Web service which has hundreds of millions of users.

An investigation into Lei was launched on Thursday after he allegedly appeared in a sex video posted by a micro-blogger on Sina Weibo.

The video was posted on Tuesday by Ji Xuguang, an investigative reporter with the Southern Metropolis Daily, who registered with his real name.

Ji accused Lei of having sex with an 18-year-old woman in the video clip, which runs for 12 seconds. He also claimed that Lei kept the woman as a mistress, and ordered police to detain her for more than a month after the sexual images were leaked onto the Internet.

Ji said on his micro blog that the video and details of Lei's scandal and evidence of corruption were first revealed by a man called Zhu Ruifeng on media.people.com.cn.

Ji said he has handed all the video material and other evidence on Lei to Chongqing disciplinary investigators, and was heading to Chongqing on Friday to help with the investigation.

The video and photographs were forwarded on several popular Internet websites and forums, and viewed thousands of times.

Ji said Lei denied being involved in the sex video, which was filmed in 2007, when Lei was deputy Party secretary of the district. Lei said the video must have been modified with Photoshop software.

"Lei told me over the phone that he was willing to 'make friends' with me, when I called him to ask for his reaction (to the video)," said Ji in one of his micro blog messages.

Ji also said he received an anonymous phone threat after he telephoned Lei.

China News Service on Wednesday also quoted Lei as denying the accusation, and saying that the images are not real.

"Do not believe it. They are all fake," Lei was quoted as saying.

Wang Xixin, a law professor at Peking University, said: "Disciplinary authorities cannot start an investigation into officials when there is no strong evidence. But online reports nowadays work well for them to gather the proof."

The Internet provides a platform for citizens to express their opinions and supervise public figures, including officials, he said.

Privacy is an issue in some incidents. However, people's legal right to know and to supervise takes precedence over officials' privacy, he added.

A report delivered by the Party's top disciplinary watchdog to the 18th National Congress of the Communist Party of China this month urged Party leaders to respond in a timely manner to "hot issues" revealed by the media or being discussed online.

Public condemnation on the Web led to the removal of safety official Yang Dacai, from the province of Shaanxi, in September, and urban administration official Cai Bin, in Guangdong province, in October.

The former was caught wearing different luxury watches in pictures posted on the Internet, while the latter was reported to own 22 apartments, far more than he can afford on his salary.

Previous investigations into officials involved in sex scandals have often led to evidence of corruption.

In 2010, a tobacco official in the Guangxi Zhuang autonomous region, Han Feng, was found guilty of corruption after his diary detailing sexually explicit episodes was posted online, allegedly by one of his mistresses.

Xinhua contributed to this story.