Yang said Dong believed he was "fundamentally innocent" for his actions on the Internet.

In Beijing, the capital, cartoonist Wang Liming was taken into custody at midnight on Wednesday and has not yet been freed, his friend, Wu Gan, told Reuters by telephone.

Wu said police told Wang's girlfriend they summoned him for forwarding a microblog post about a stranded mother holding a baby who had starved to death in the flood-hit eastern city of Yuyao.

"Suppression of this kind by the Chinese government is of no use," Wu said. "Rumours arise because there's no freedom to communicate on the Internet. Arresting people will not solve the problem because the problem does not lie with the people, but with the government."

The detentions come slightly over a month after China unveiled tough measures to stop the spread of what it calls irresponsible rumours, threatening jail terms of three years if untrue online posts are widely reposted.

China's top court and prosecutor have said people will be charged with defamation if online rumours they create are visited by 5,000 internet users or reposted more than 500 times.

Liu Hu, a Chinese investigative journalist accused of corruption was arrested on a defamation charge late in September, his lawyer said last week.

The Internet clampdown belies the insecurity of the leaders of the ruling Communist Party, said Bo Zhiyue, a professor of Chinese politics at the National University of Singapore.

"They are trying to send China back all the way to the Stone Age," Bo said. "Where is the hope for political reform? Zero."