In a landmark ruling, a district court Monday sentenced a left-wing lawmaker to 12 years in prison for plotting an armed rebellion against the South Korean government in case of an inter-Korean war.

Rep. Lee Seok-ki, affiliated with the minor opposition Unified Progressive Party , was found guilty of conspiring with members of a clandestine organization to topple the Seoul government if a war with North Korea broke out.

The Suwon District Court in Suwon, south of Seoul, also stripped the 52-year-old legislator of his civic rights, such as suffrage, for 10 years following his eventual release from prison.

It is the first time that a sitting member of parliament was convicted of the rare charges of plotting an armed uprising to overthrow a democratically elected government.

Court documents showed that Lee talked with about 130 other members of the secret underground organization, Revolutionary Organization, during late-night secret meetings in central Seoul last May about blowing up key infrastructure in South Korea, including communication lines and railways.

Past military-backed governments used insurgency charges to suppress political dissidents. However, there have been no indictments over insurgency plots or other similar anti-government charges in recent years since democratically elected leaders replaced the country's past military dictators.

In 1980, former South Korean President Kim Dae-jung, the winner of the Nobel Peace Prize in 2000, was put behind bars for the same charge but later was acquitted in a retrial.

The UPP lawmaker flatly denied the accusations, saying that the trumped-up charges were brought against him by the National Intelligence Service (NIS) as a means of distracting public attention from an investigation into allegations that it meddled in the 2012 presidential election.

In September, the NIS raided the UPP office and arrested Lee and seven other UPP members.

The National Assembly soon tabled a motion, introduced by the ruling Saenuri Party, that calls for expelling Lee. His expulsion is subject to two-thirds approval from the ethics committee and then two-thirds approval from the full National Assembly.

In an unprecedented move, the government also filed a petition with the Constitutional Court calling for the disbandment of the UPP.

On Monday, Lee was also found guilty of a separate charge of sympathizing with North Korea, in violation of the South's anti-communist National Security Law.

Enacted in 1948 to fight communism, the draconian security law bans any "anti-state" activities that attempt to praise, encourage or propagandize North Korean political ideals.

The lawmaker made remarks sympathetic to North Korea and sang North Korea's "revolutionary" propaganda songs before hundreds of members who attended the organization's meetings held between March and August of last year, court documents showed. Lee also possessed publications praising the communist regime.

In 2002, Lee was previously sentenced to two years and six months in prison for playing a part in a pro-North Korea organization but was later released on presidential pardon. He was elected to the National Assembly on a proportional representation ticket in 2012 general elections. (Yonhap)