China's two biggest microblog sites resumed normal service yesterday after a three-day ban on posting comments, amid the worst high-level political crisis in years.

The temporary suspension by Sina's and Tencent's followed a flurry of rumours online about the downfall of a prominent Communist Party figure, Bo Xilai. The authorities have closed a dozen websites and detained six people for circulating rumours of a coup.

The two companies said in statements on their websites that the shutdown was aimed at "cleaning up" illegal and harmful information posted on some microblogs, but gave no details. During the suspension, users could post on their own microblogs but were barred from making comments on others' accounts.

The clampdown underscores the party's anxiety over an internet-savvy public who are eager to discuss political events despite censorship and threats of punishment. Sina and Tencent say they have a total of nearly 700 million microblog accounts.

Mr Bo, a populist once seen as a contender for a seat on the party's ruling nine-member Politburo Standing Committee, was dismissed on 15 March as party secretary of Chongqing. State media have provided little information on Mr Bo, fuelling speculation that spiralled into talk of troop movements and gunshots in Beijing.