Authorities in Beijing have detained six people and closed a number of websites for spreading political rumors online in the run-up to a key leadership transition later this year, official media reported.
Two hugely popular Twitter-like services in China have suspended comments on individual microblogs after the companies were punished for allowing rumors of a political coup in Beijing to spread online.
Sina and Tencent both suspended the comment functions on their microblog, or "weibo," services at the weekend. The ban will run until Tuesday, the English-language China Daily said on its website.
The authorities have also closed 16 websites in recent days for propagating the same sorts of rumors, which have flooded the Chinese Internet since the March 15 ouster of former Chongqing Communist Party chief Bo Xilai.
Bo's whereabouts are still unknown, and the absence of any official statement on his fate have fueled speculation that China's security chief Zhou Yongkang, who is believed to have been Bo's highest-ranking political supporter, tried to stage a coup in Beijing.
According to Beijing police and the State Internet Information Office, the websites were closed for spreading rumors of 'military vehicles entering Beijing' and 'something amiss in Beijing,' the paper said.
It said the rumors "were fabricated by some lawless people recently."
The Beijing municipal public security bureau said the six people had been detained for "allegedly fabricating and spreading the above-mentioned rumors, particularly through microblogging posts," China Daily said.
A state information official also confirmed that Sina and Tencent's microblogging services had been "criticized and punished accordingly" by Internet information administration authorities in Beijing and Guangdong, the paper said.
The crackdown came amid reports that a billionaire associate of Bo's from his time as Party secretary in the northeastern port city of Dalian was placed under investigation by Party discipline inspection officials for suspected "economic crimes."
Xu Ming, chairman of the chemical company Dalian Shide Group, was detained over alleged involvement in economic crimes, the National Economic Weekly reported on Saturday.
Xu, who was named the eighth richest person on China's mainland in 2005 by Forbes, also sits on the board of the Bank of Dalian.
He was detained by the Central Commission for Discipline Inspection on March 15, the same day that Bo's removal from his position in Chongqing was announced.
U.S.-based political activist Liu Nianchun said it was likely that the probe into Xu's financial affairs would turn up some evidence linked to Bo.
"Bo Xilai and Xu Ming have been collaborating for a very long time," Liu said. "They will be hoping to bring Bo down by using economic and corruption charges."
"This should have happened a long time ago, because it's clear that he did even more of this sort of thing than [disgraced Beijing mayor] Chen Xitong and [disgraced Shanghai Party chief] Chen Liangyu."
Retired Shandong University professor Sun Wenguang said Bo's investigation would be a good thing for the fight against corruption in China.
"If they can show links between Bo Xilai, a Politburo member and Chongqing Party secretary, and local business, and make them plain for everyone to see, then this will be a good thing for the fight to clean up China's government," Sun said.
"The fact that they have started to investigate entrepreneurs from Dalian suggests that there is a relationship with Bo Xilai," he added.
Reported by Yang Jiadai for RFA's Mandarin service. Translated and written in English by Luisetta Mudie.