SEOUL, Feb. 3 -- Prosecutors in South Korea on Monday sought a 20-year prison term for a lawmaker of the minority political party, which has been considered as a blind follower of the Democratic People's Republic of Korea (DPRK).

The prosecution asked judges at the final trial to sentence Rep. Lee Seok-ki of the left-leaning Unified Progressive Party (UPP) to 20 years of imprisonment for treason charges. Prosecutors also demanded the suspension of Lee's rights such as suffrage for 10 years after his release from jail.

Lee was accused by the prosecution of plotting to overthrow the government as he talked with members of the Revolutionary Organization (RO), claimed as a secret anti-governmental society, about destroying infrastructures such as railways and communication lines.

The leftist legislator was also charged with inciting sedition as Lee led the clandestine organization as well as with violating the anti-communist National Security Law as he praised the DPRK by singing Pyongyang's military march songs.

Prosecutors said during the trial that Lee entered the parliament to revolutionize South Korea in accordance with the DPRK's ideology and revolutionism and abused his status as a lawmaker to order RO members to prepare for a riot and military warfare.

Long-term isolation of Lee from the society would be the only way to prevent another conviction, the prosecution added.

Prosecutors also sought a 15-year prison term for another five members of the minority party for treason charges together with Lee, while demanding a 10-year imprisonment for the other member.

Lee was arrested in early September last year on rebellion conspiracy charges, becoming the first lawmaker to face detention on treason charges while in office. Lee had been described by some conservative news media as one of the most dangerous pro-Pyongyang figures.

Lee, who had done underground activities, entered the mainstream political circle by winning a parliamentary seat in April 2012 as a proportional representative of the UPP.

The minority party was in danger of being disbanded as the Justice Ministry submitted its petition in November last year for dismissing the UPP to the constitutional court for the first time in the country's history.

If more than six judges among nine favor the request within six months, the UPP will be disbanded and the alternative party to the UPP will be banned from being organized.