BEIJING (AP) — A Communist Party leader has told China's Internet companies to tighten control over material online as Beijing cracks down on dissent and tries to block the rise of Middle East-style protests.

The party secretary for Beijing, Liu Qi, issued the warning following a visit this week to Sina Corp., which operates a popular microblogging site, according to the party-published newspaper Beijing Daily.

Internet companies should "strengthen management and firmly prevent the spread of fake and harmful information," Liu was quoted as saying after the visit Monday to Sina. He said companies should "resist fake and negative information."

Communist authorities encourage Internet use for education and business but are uneasy about its potential to spread dissent, especially after social networking and other websites played a key role in protests that brought down governments in Egypt and Tunisia.

Beijing is in the midst of one of its most sweeping crackdowns on dissent in years and has detained or questioned hundreds of activists, lawyers and others.

The government tries to block access to foreign websites deemed subversive and Chinese operators of websites where the public can post comments are required to watch the material and remove any that violates censorship rules.

The government's censorship rules prompted Google Inc. to close its China search engine last year. Mainland users can see Google's Chinese-language search site in Hong Kong but access is slower and the company's China market share has shrunk.

The report on Liu's warning gave no details of how Internet companies were expected to change their management.

Employees who answered the phone at Sina referred questions to a spokeswoman who did not answer her phone.

With Liu during the visit were Sina CEO Charles Chao and Kai-fu Lee, a former boss of Google's China unit who runs a technology investment company, according to the Beijing Daily.

Chao told Forbes magazine in March that Sina's microblogging site, Weibo, has at least 100 employees monitoring content 24 hours a day. The company said in May that the number of Weibo users had passed 140 million.

Also this week, the Beijing Internet Media Association, a government-sanctioned industry group, called on its 104 member companies to police Internet content, possibly prompted by Liu's order.

"Propaganda guidance to the public should be led toward a correct direction," the appeal said, according to the Beijing Daily. "Online news should be trustworthy and should not spread rumors or vulgar contents."

Liu, the party secretary, also visited the headquarters of Youku.com Inc., a video portal, and talked with CEO Victor Koo, the report said.

China has the world's biggest online population, with 485 million Internet users as of June 30, according to the government-sanctioned China National Internet Information Center.

Meanwhile, a major Chinese Internet commerce platform, Taobao, has told merchants that use its service to stop selling virtual private network and other software that allows Web surfers to avoid government filters.

Taobao, part of Alibaba Group, said it acted after finding VPNs were being used to visit foreign websites illegally. A company spokesman said Tuesday it took the action on its own without receiving government orders.