The requirement to obtain government permission before any newsgathering in the city center is the latest sign of official jitters sparked by Internet calls for popular protests each Sunday similar to those that have toppled authoritarian leaders in Egypt and Tunisia and continue to roil North Africa and the Middle East.

Despite three decades of economic liberalization and the withdrawal of Communist control over many parts of China’s increasingly prosperous and diverse society, the one-party state brooks no challenge to its rule and routinely harasses and imprisons its critics.

On the third Sunday since the anonymous Internet postings first appeared, no apparent demonstrations occurred in Beijing or Shanghai, though like previous weeks the designated sites drew onlookers and heavy security. In Shanghai, as a cold rain fell, police detained at least 17 foreign reporters for showing up at the protest site, People’s Square, because they did not have prior permission to be there.

At a hastily called news conference in Beijing, Li Honghai, vice director of the city’s Foreign Affairs Office, said reporters must apply for and receive government permission to conduct any newsgathering within the city center.

Li’s announcement, which he described as a new interpretation of existing rules, makes explicit restrictions that police began imposing more than a week ago following online postings for Sunday protests at designated spots in Beijing, Shanghai and other Chinese cities. In the past week, police have followed foreign reporters in Beijing, and in some cases stopped foreign TV news crews from filming even unrelated stories because they lacked permission.

The requirement for permission — delivered only verbally and not in writing — shows how nervous China’s leaders are about the calls for protests and how determined they are to prevent them spreading via the international media, text messaging, and social networking sites as they did in the Middle East. China already blocks Facebook and Twitter and heavily monitors their Chinese equivalents for any content deemed subversive.

Beijing officials used the news conference to denounce the Internet appeals as an attempt to undermine China’s stability.

"All clear-minded people will know that these people have chosen the wrong place and have the wrong idea. The things they want to see take place have not and cannot occur in Beijing," said city government spokeswoman Wang Hui.

Requiring permission marks a rollback of more relaxed regulations governing foreign reporters that were first instituted for the 2008 Beijing Olympics and then made permanent. Those rules dropped an earlier requirement of official permission to report, and instead said reporters only needed the consent of the "work unit" or person they wanted to interview.

At the two designated protest sites in Beijing, both busy shopping streets, large numbers of uniformed and plainclothes police patrolled and scrutinized passers-by. Foreign reporters who managed to pass or avoid police checkpoints at Wangfujing were followed and videotaped.

At the other Beijing site, Xidan, officers checked identification cards of people and questioned and filmed journalists outside the nearby subway station. Reporters were told to leave and were made to board a parked bus where their press accreditation details were recorded.

Police also swarmed over a shopping mall in Beijing’s university district Sunday afternoon and disrupted some cell phone services after large numbers of students congregated there, witnesses said.

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Associated Press writers Gillian Wong and Charles Hutzler in Beijing and Elaine Kurtenbach in Shanghai contributed to this report.