A popular Twitter-like service in China has contacted millions of users warning them to ignore false reports, in a sign of growing official unease over the rise of social networking sites. Sina's micro-blogging site Weibo sent at least two messages on Friday to refute rumours, including one that the suspected murderer of a 19-year-old woman had been released on bail because of his father's connections. Sina said the bloggers who had posted the false reports would have their accounts suspended for one month and would not be able to send messages or be followed during that period. The notice came after a top Communist Party official visited the offices of Sina and Youku, China's answer to Youtube, and urged Internet companies to stop the spread of "false and harmful information", the Beijing Daily reported Tuesday. China -- which has the world's largest online population with 485 million users -- constantly strives to exert its control over the Internet, blocking content it deems politically sensitive as part of a vast censorship system. But the rise of China's weibos -- microblogs similar to Twitter, which is banned by the communist authorities -- has exposed the difficulty of controlling access to information. During the visit to Sina and Youku, Beijing's Communist Party chief Liu Qi said Internet companies should "ensure the authenticity of information... to create a healthy online media atmosphere", the Beijing Daily report said. Chinese people are increasingly turning to weibos to vent their anger over government corruption, scandals and disasters in a country where authorities maintain a tight grip on the media. After a deadly train crash in July, Sina's Weibo users sent millions of messages criticising the official response to the disaster, which killed 40 people and forced the government to halt the expansion of high-speed rail. The scale of the response appeared to take authorities by surprise. Shortly after the accident, the People's Daily, the mouthpiece of China's Communist Party, urged officials to use the weibos more to communicate with the public.