South Korea's military will launch an investigation into soldiers who posted pro-Pyongyang messages at an online message board praising North Korea, an official said Monday.

The defence ministry is investigating seven or eight soldiers who wrote postings praising the communist North's leader Kim Jong-Il or commented on articles by others, a ministry spokesman said.

The website, started by a 43-year-old South Korean, had several thousand members until police arrested its creator following the North's deadly bombing of a South Korean border island last November.

He was given a suspended jail sentence for violating a national security law that bans publications praising North Korea and unauthorised contact with its people.

The website was later shut down.

Chosun Ilbo newspaper reported Monday that several soldiers had posted articles pledging allegiance to Kim and his son and heir apparent, Jong-Un.

The ministry spokesman said that apart from the seven or eight, several dozen other soldiers are being investigated for signing up for membership of the Internet community board.

"Most of them, except for the seven or eight problematic ones, appear to have signed up out of sheer curiosity.... We will launch a full investigation on how much they were involved in the community," the spokesman told AFP.

The two Koreas have technically remained at war since their 1950-53 conflict ended only with an armistice instead of a full peace treaty.