Some of China's leading internet sites have been punished for failing to control what the government terms "harmful information."

Beijing carried out one of its largest law-enforcement check-ups of the internet ahead of the 16th Chinese Communist Party National Congress, which meets in the autumn.

Ten major domestic web portals were targeted, with Tom.com, Sina and FM365 due to undergo regular inspections over the next three months.

Web sites controlled by foreign owners were set up when the dot.com boom hit China, Hong Kong broker Howard Gorges told the BBC's World Business Report.

"China made it very clear it would vet what was shown on those sites," he said.

Banned content

The onus was on the operators of the sites to screen the content and ensure nothing was published that the Chinese government would consider 'harmful'.

The authorities ban rumours, libel, subversion, sabotage of national security, the promotion of cults and feudal superstition, as well as pornography, violence and gambling.

It is unclear how long the internet crackdown will continue, or whether there will be a gradual liberalisation of the network.

The latest controls coincided with China's loss in its World Cup football debut against Costa Rica - a performance that prompted furious criticism of the national team in internet chat rooms.