Chinese Internet users could face three years in prison for writing defamatory messages that are then re-posted 500 times under regulations announced Monday amid a broader crackdown on "online rumours".
Web users could also be jailed if offending posts are viewed more than 5,000 times under the new rules, which appear to be part of a controversial campaign against online chatter, which has seen companies, bloggers and journalists targeted.
China has the world's largest population of Internet users and authorities seek to keep close control on the country's hugely popular weibo microblog sites, where a number of officials have been exposed for corruption.
The new guidelines announced by the country's most senior court and its top prosecuting body stipulate that netizens may be charged with defamation if "defamatory information" they post reaches the quotas on viewings or re-posts.
Posts will also be deemed defamatory if the information causes "suicide or self-mutilation... of the parties involved", the new law adds.
The maximum sentence for defamation in China is three years in prison, the official Xinhua news agency said.
The new regulations also contain rules against extortion, blackmail and provoking online arguments.
In recent months a wide-ranging clampdown on "online rumours" has been launched by Beijing, with hundreds of people questioned or detained as a result.
Last month officials told Internet celebrities with millions of online followers to "promote virtues" and "uphold law" online.
Among those rounded up in the clampdown are 27 people from the central city of Wuhan who were detained after police broke up an "online rumour speculation company".
Chinese-American billionaire blogger Charles Xue was also arrested this month for suspected involvement in prostitution and "group licentiousness".
Xue has attracted 12 million followers on Sina Weibo, China's equivalent of Twitter, regularly posting reform-minded comments on a variety of sensitive issues.
Last week Chinese official Yang Dacai was jailed after netizens posted pictures of him online with expensive watches, triggering a corruption inquiry.
But analysts questioned whether such widely-circulated revelations could be repeated as authorities rein in Internet chatter.
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