China started a sweeping crackdown of its vibrant social-networking media over the weekend, detaining six people, closing 16 websites and shutting off the comment function for two gigantic microblog services.

The campaign, which was announced late Friday and put in place in stages through Saturday, was directly linked to the political instability that has gripped China since one of its most charismatic politicians, Bo Xilai, lost his post in March. That spurred rumours of a coup, which the government-run Xinhua news agency cited as the reason for the measures.

Xinhua quoted an official with the State Internet Information Office as saying that the sites had spread reports of ''military vehicles entering Beijing and something wrong going on in Beijing.''

The reports, which Xinhua said were carried on the sites meizhou.net, xn528.com and cndy.com.cn, stemmed from disagreements among senior leaders over whether to remove Bo, who is being investigated over accusations of corruption and abuse of power. One of his backers, the senior leader Zhou Yongkang, was said to be behind the planned coup, although most Chinese analysts have discounted this as a fabrication.

In addition to the six detainees - whose names were not released - Xinhua said others were ''admonished and educated'' and had promised to ''repent.''

The sites that were closed were relatively minor players in China. More noticeable for most Chinese was the decision to shut off the commenting services for microblogs run by the Sina Corp and Tencent Holdings, which each have 300 million registered accounts.

On Sina's Weibo service, users who tried to comment on posts after 8am Saturday were greeted with a message saying that microblogs contained ''many rumours and illegal, destructive information.'' The shutdown was necessary, the notice said, ''to carry out a concentrated cleanup.'' It said comments would be allowed starting Tuesday morning.

The measures allowed users to post, but not comment on others' posts. Even though the actions are linked to the Bo Xilai affair, analysts say the government began to take steps last July, when a high-speed rail crash led to an outpouring of reports and criticism that cast doubt on the government's version of events. Within a week, most critical posts were deleted.

Later last year, the government announced that all microbloggers would have to register under their real name, a measure that was supposed to be enforced by the middle of March. Currently, users with pseudonyms can still post, but analysts say they expect the rule to be slowly enforced over the coming months.

The measures come during a difficult time for China's leadership. Besides the scandal swirling around Bo, the party is preparing for a once-in-a-decade leadership transition later this year that has stirred up rumours and allegations.

Despite the official rationale that the measures are justified to promote accuracy, analysts note that China's official news media itself often is inaccurate and presents only the government's position.

''The whole idea of rumours and interest in accuracy is a ruse,'' said David Bandurski with the China Media Project at Hong Kong University. ''It's a moniker for control.''

The New York Times