BEIJING (REUTERS) - Chinese Internet firm Sina Corp has been stripped of its online publication licence after being targeted in a pornography crackdown, state media reported, prompting a 4.5 per cent drop in its share price.

Twenty articles and four videos posted on Sina.com contained"lewd and pornographic content", the official Xinhua news agency said, citing a statement by the National Office Against Pornographic and Illegal Publications.

"As of result, the State Administration of Press, Publication, Radio, Film and Television revoked the company's two crucial licences on Internet publication and audio and video dissemination," Xinhua said.

China has shut down more than 100 websites carrying pornography and closed thousands of accounts on social media sites in a campaign to clean up the Internet, the news agency reported earlier this week.

Pornography is illegal in China, but some overseas critics are concerned that the crackdown on material deemed obscene is the latest government attempt to tighten its grip on the Internet and will be used in broader censorship of websites.