President Kim had promised an earlier repressive policies

Grand National Party members say they removed a number of materials from Room 529 as evidence to back up their claims of spying.

"It clearly proves that the intelligence agency has been secretly inspecting legislators by stationing an office inside the Assembly building," a GNP spokesman told reporters after reviewing the material.

The National Intelligence Service has condemned the opposition's behaviour as illegal and says it will take legal action against them.

'Secret documents'

BBC Seoul Correspondent Andrew Wood: If true the allegations would be embarassing for the government

In a press statement, the agency accused the GNP of "seizing secret national documents."

The NIS says Room 529 is in fact an archive for the parliamentary intelligence committee and that the allegations are simply untrue.

On Wednesday, the opposition party held the second day of a sit-in protest at the National Assembly demanding an apology from President Kim Dae-Jung for the alleged illegal surveillance.

Embarassing allegations

The BBC's correspondent in South Korea, Andrew Wood, says if the allegations are allegations it could be very embarrassing for the government - who promised a break with Korea's repressive past when they were elected one year ago.

Despite attempts to reform the security agency, it is being accused of continuing its old behaviour by spying on politicians in parliament.

But when the present opposition were in power, the intelligence service tried to assassinate the man who is now president, Kim Dae Jung.