The ban applies to Sina Corporation's Weibo and a similar service run by Tencent Holdings, Lee said yesterday on Twitter, where he has around one million followers.

"I've been silenced on Sina and Tencent for three days, so everyone can come here to find me," he said, without giving a reason.

Lee, who is now chairman and chief executive of Innovation Works - a Beijing-based technology-business incubator - declined to elaborate on what he said.

Lee has used Weibo to complain about China's internet controls.

A post last Saturday summarized a Wall Street Journal article about how slow speeds and instability deter overseas businesses from locating critical functions in the mainland.

Last month, he posted support for the Guangzhou-based newspaper staff during a standoff with government censors.

"You can be outspoken with one or two million fans, or a few hundred thousand, but 30 million followers is like a provincial radio or TV station," said Bill Bishop, an independent technology industry consultant in Beijing.

"I don't know how many other people have that many."

Liu Qi, a spokesman for Sina in Beijing, declined to comment.

Jerry Huang, a director of investor relations for Tencent in Shenzhen, did not respond to a message seeking comment.

China controls access to the internet, including blocking Twitter, Facebook and Google's YouTube, to limit criticism of the Communist Party.

Lee said in a September speech at a World Economic Forum conference in Tianjin that the rising use of social media in the mainland is one way of tackling corruption.

BLOOMBERG