S. Korea prosecutors seek 20 years in MP sedition trial
Lee Seok-Ki (C), a leftist lawmaker from South Korea's United Progress Party, waves to supporters after a parliamentary vote on a government motion for his arrest on sedition charges in Seoul on September 4, 2013 - by Jung Yeon-Je
Prosecutors also asked judges to strip United Progressive Party (UPP) MP Lee Seok-Ki of his civic rights for 10 years following his eventual release from prison.
The sedition charges levelled against Lee are rarely used, especially against a sitting member of parliament.
After parliament voted to lift his immunity from arrest, Lee, 52, was charged in September last year with plotting an insurrection to overthrow the government.
"(Lee) deserves heavy punishment for ordering members of his group to prepare for riots and military warfare," Yonhap news agency quoted the prosecution as saying in closing statements to the court in Suwon, south of Seoul.
The prosecution is also seeking jail terms of up to 15 years for six UPP members being tried on similar charges to Lee.
The lawmaker was accused of seeking a socialist revolution in support of North Korea as head of an underground radical group that formed the core of his party.
The verdict in the case is expected within two weeks.
According to prosecutors, Lee was caught on tape telling members of his group to prepare attacks on South Korea's communication lines and railways in case of war with the North.
Lee has dismissed the charges as fabricated, insisting his remarks in May were prompted by worries about a possible US invasion of North Korea.
He has also described himself as the victim of a "witch hunt" by South Korea's spy agency, the National Intelligence Service.
South Korea's constitutional court has yet to make a decision on a government petition to disband Lee's party, which fielded a candidate in the 2012 presidential race.
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.