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China's internet watchdog has banned web users from posting messages under the names of famous people.

The Cyberspace Administration of China (CAC) said it was combating the "vulgar culture" of using names like Barack Obama, or those of Chinese officials.

The CAC is a Communist Party organ overseen by President Xi Jinping, so its rules will carry more force than those of other regulators.

Similar restrictions by other bodies have been sidestepped by web firms.

The CAC announced a series of measures that would be in force from 1 March.

It said nicknames should not include information that could violate the constitution, subvert state power, undermine national security or promote rumour-mongering.

In addition, web users must sign a pledge to avoid "illegal and unhealthy" internet activity, and register accounts under their real names even if they want to post under nicknames.

CAC's head of mobile internet, Xu Feng, promised that the new regulations would not limit users' freedom.

"This does not restrict internet users, instead it protects their legitimate rights," he said.

Real-name registration has been a goal of the Chinese authorities for years.

The State Internet Information Office (SIIO), an organ of the State Council, passed similar rules in 2012.

The office announced last month that it would step up its efforts to enforce users of microblogs, smartphone chat apps to register with real names.

But campaigners have decried the regulations as a crackdown on free speech, and the SIIO has been largely unable to enforce the measures.

With some 649 million people online, there are more internet users in China than any other country.

However, Beijing has been gradually tightening its control over the web and has the world's most well-developed censorship system, known as the Great Firewall.

International websites such as Facebook are banned, and last month China successfully blocked several Virtual Private Network (VPN) services that were allowing people to skirt around the restrictions.

Internet comments that appear to criticise or undermine the government are monitored particularly carefully.

Last month 133 accounts on the messenger service WeChat were shut down for "distorting history", state media said.