TOKYO - Japan's top Internet forum 2channel was offline Tuesday after an apparent mass hacker attack from South Korea over slanderous comments on their Olympic figure skating queen Kim Yu-Na.

South Korea's Yonhap news agency reported that more than 10,000 users had launched a "concerted cyber offensive" and coordinated their attacks through web communities since Monday against the popular site www.2ch.net.

The site, launched in 1999, allows users to post comments on hundreds of topics, from politics and sports to entertainment and manga cartoons, without providing a user name, a model meant to boost online freedom of speech.

But the site has repeatedly become a forum for right-wing nationalists and users posting xenophobic slurs, especially against South Korea and China.

The 2ch forum is Japan's largest online bulletin board by number of users and page views, according to Internet research firm NetRatings Japan.

The site was not accessible on Tuesday, but its search lists showed Japanese-language attacks had earlier been posted against Kim, who beat Japanese rival Mao Asada to take gold at the Vancouver Winter Games.

South Korea's JoongAng Daily reported online that the cyber war was launched on Monday, the anniversary of a 1919 uprising against Japanese colonial rule that became known as the March First Movement.

South Koreans have often been angered by comments on the messaging forum, including one that called a deadly attack against a South Korean college student in February in Irkutsk "Russia's good deed", Yonhap reported.

The 2ch forum has often drawn controversy at home as some of its anonymous users have posted death threats and verbal attacks against high-profile figures that have led to legal action against the site's operators.