The mainland’s internet police have struck again, closing down or suspending several popular microblogs in the past week as they step up a crackdown on online discussion of politically sensitive issues.

One well-known blogger, Wang Xiaoshan , said friends told him yesterday morning that his Sina.com microblog had been closed down. He said he had no idea what was behind the closure or what he had done wrong.

Wang said he had written more than 36,000 postings and his microblog had attracted 570,000 followers.

He said he had also received a notice from Sina.com management yesterday, but could not disclose its contents.

“But I can tell you one thing for sure, the closure was not carried out by Sina.com voluntarily,” he said. “But I am not shocked by the decision, given that anything can happen in this country.”

Mainland censors introduced a real-name registration requirement for microbloggers in March, a…