The police chief of Beijing has warned that Web users who "attack" leaders of the Communist Party of China and the country, or the current system will be severely punished, raising concerns over control of online speech.

Fu Zhenghua, chief of the Beijing Public Security Bureau, made the remark at a meeting on cleaning up cyberspace on Tuesday. The one-month cleanup campaign is mainly aimed at protecting and creating a healthy cyberspace for minors.

Fu said the police have set up platforms to report offences on major microblog sites to reinforce oversight.

Three of the country's four top microblog service operators are based in Beijing, including the most popular site Sina Weibo.

Those who make up and spread political rumors, attack the Party and government leaders and the system will receive a public warning or severe punishment according to law, said Fu, according to the Beijing News.

However, he didn't specify what constitutes a political rumor or an attack.

As a result, on microblogs, users are asking the police chief to define what constitutes an "attack" or a "political rumor." It also raised people's concerns over whether the cleanup campaign will mute online criticisms of the government.

Zhang Qianfan, a law professor at Peking University who specializes in constitutional law, said that there are no criminal or administrative laws prohibiting people from criticizing the government.

"(The chief's remarks) are quite vague and broad, and it might lead to abuse of power in punishing people," said Zhang.

Article 41 of the Constitution of China stipulates that citizens have the right to criticize or give suggestions to any government agencies or staff members, but should not make up or twist facts.

"People have the right to oversee the government and have every right to express their emotions or sentiments or opinions, no matter what kind of opinions they are," said Yu Guoming, director of the Institute of Public Opinion under the Renmin University of China.

With over 538 million Web users and at least 250 million microblog users, the Internet has become an important channel for Chinese citizens to voice their grievances, anger and hopes, and sometimes touch upon sensitive issues.

The authorities are hearing a very different and often negative public opinion than was the case in the past, and they have to adapt to it, said Yu.

The explosive growth of online information dissemination has also led to a number of rumors circulating on the Internet.

The best way to refute rumors is through transparency, said Zhang. "If the government could be more open when dealing with certain things, the rumors would easily be dismissed."