BEIJING, Oct. 9 -- Police in Beijing have nabbed some 30,000 suspects involved in cyber crimes in an online crackdown that began in 2011, according to the latest statistics.

According to Beijing's public security bureau, about 17 million illegal online messages were deleted in the three-year campaign, which also led to the detainment of more than 50 suspects implicated in terrorism activities.

The clamp-down targeted cyber crimes, hackers, online rumor-mongering as well as terrorism and violent content, according to the bureau. By June this year, police had deleted 3,300 terrorism-related messages and 728 audio and video files and e-books, the bureau said.

Police also stepped up penalties for operators that violated Internet laws and regulations. In 2011, around 1,000 operators were punished in accordance with the law. The number soared to 11,000 two years later.

Official data showed that by the end of 2013, Beijing was home to more than 900,000 licensed websites, with about 70 percent of China's major web portals located in the capital city, and an online population exceeding 16 million.