Hackers have raided two Japanese government web sites, leaving a message on one of them attacking Japan over the 1937 Nanking massacre.

The homepage of Japan's Management and Coordination Agency was replaced with derogatory messages about the Japanese in what is thought to be the first hacking of the country's government computer system.

According to the Jiji news agency, hackers left a message on the web site in Chinese, saying: "The Chinese people must speak up to protest the Japanese government for refusing to acknowledge the historical misdeed of the 1937 Nanking Massacre."

Hundreds of thousand of civilians were massacred by Japanese troops during the 1937-38 occupation of the central Chinese city.

Last week, a group of ultra-rightwing Japanese held a conference in Osaka to deny the massacre, also called the Rape of Nanking.

The Chinese government lodged protests about the gathering. But the Japanese government, which acknowledges that the incident was no fabrication, failed to ban the meeting.

Hackers also hit the web site of Japan's Science and Technology Agency, forcing it to suspend access to the site.

E-mail bomb

After breaking into the web site, the hackers posted a derogatory message and a trick to gain access to the web site of an overseas adult magazine.

The message was signed off with the words "Brazil p00 hackerz".

The agency was the target of an "e-mail bomb" last month when it received several hundred identical e-mails.

Government spokesman Mikio Aoki said the government would launch an extensive investigation into the hacking incidents and would possibly seek help from the US which was more advanced in dealing with hackers.

The government had yet to ascertain whether the two incidents were related.