The war between Chinese and American hackers that led to the White House Web site being shut down was illegal, Chinese Internet security officials have said.
But they did not indicate whether action would be taken against the mainland hackers involved.
The warning signals that the Chinese Government probably wants to draw a line under the week of attacks in which dozens of US and Chinese sites were defaced.
A spokeswoman for the Internet Safety Bureau, under the Public Security Ministry, said: 'Such attacks are not legal. It is against the law to enter other people's systems.'
The statement has fuelled speculation that the cyber-battle may be coming to an end.
Intellectuals say it is unlikely Beijing will take any action against the hackers.
American officials have complained that such a large-scale operation indicates the Government either turned a blind eye to or may even have encouraged the hackers, a claim denied by Chinese officials who insist it was a spontaneous product of anti-US resentment.
The cyber-battle took place against a background of deteriorating Sino-US relations and during the week-long May Day holiday, which meant hackers had more time on their hands.
The call to halt the attacks came a day after people.com, the official Web site of the People's Daily , published an editorial condemning the Chinese-initiated hacking as 'Web terrorism'.
'The attacks by the Honker Union of China, or Red Guests, on US Web sites are unforgivable acts violating the law,' the editorial said. 'It is Web terrorism.'
The strongly worded editorial warned that the activities by Red Guests, a group of patriotic anti-US hackers, could be disastrous for China's Internet security. It was posted on all of China's major Web sites yesterday.
'We understand the passion of these hackers but we do not endorse their way of expressing it,' the director of people.com's editorial office, Liao Hong, said. 'We do not want to offend patriotic Web surfers but it is important we alert the public to the risk of such acts and prevent further disasters.' He said the cyber-war was a lose-lose game.
The vice-president of the Beijing Broadcasting Institute, Su Zhiwu, said Sino-US conflicts should be resolved through diplomatic channels, not hacking manoeuvres.
Pro-Chinese hacking peaked on Friday - the anniversary of the May 4, 1919, nationalism movement - with at least 600 US Web sites defaced. US Internet experts said pro-US hacker attacks had averaged between 20 and 30 a day.
Chinese Internet experts said mainland sites lagged behind their US counterparts in their ability to respond to attacks and repair damage.
ChinaByte.com, a Chinese technology Web site, had reported that the Chinese hackers' campaign was planned during an online meeting called by the Honkers Union.