SEOUL - South Korean prosecutors on Thursday formally charged a leftist lawmaker with plotting an armed revolt in support of North Korea.
United Progressive Party MP Lee Seok Ki was charged under the tough National Security Law - a sweeping piece of legislation enacted in 1948 to guard against espionage and other threats from a belligerent North Korea.
Although the law has been amended numerous times, international rights groups have criticised its continued potential for abuse as a form of political repression.
The sedition charges levelled against Lee are rarely used, especially against a sitting member of parliament.
Prosecutors said they would provide evidence of Lee telling an underground radical group in May to prepare attacks on South Korea's communication lines and railways in case of a war with the North.
Lee made his alleged remarks at a time of soaring military tensions between North and South Korea. The National Intelligence Agency (NIS) detained Lee three weeks ago after the national assembly voted to lift his parliamentary immunity from arrest.
Three of Lee's supporters were also arrested on similar charges of plotting an armed insurrection.
Lee has dismissed the sedition charges as fabricated, insisting he is the victim of an NIS "witch hunt".
His party has accused the agency of using the case to deflect attention away from a scandal involving NIS agents who sought to smear the opposition candidate in last year's presidential election.
Lee has been in trouble for his political views before.
In 2002 he was sentenced to two and a half years for anti-government activities. He received a presidential pardon later the same year.
North Korea has criticised the arrest of Lee and his supporters, and cited it as one of the reasons for its decision to postpone a planned reunion for family members separated by the Korean War.