A leftist lawmaker, on trial for rebellion charges, flatly denied Tuesday that he had plotted to overthrow the South Korean government in the event of an inter-Korean war.

Rep. Lee Seok-ki of the minor opposition Unified Progressive Party (UPP) has been indicted on charges of conspiring and inciting a rebellion, as well as sympathizing with North Korea, in violation of the South's anti-communist National Security Law, prosecutors said.

"(I) have never intended to conspire to stage a rebellion," Lee said during his first trial at the Suwon District Court in Suwon, south of Seoul.

Lee and six other key party members are accused of leading a clandestine organization called the Revolutionary Organization (RO), prosecutors said.

The 51-year-old Lee allegedly talked with about 130 other RO members during late-night secret meetings in central Seoul in May about blowing up key infrastructure in South Korea, including communication lines and railways. He pledged to side with the North in case of a war on the Korean Peninsula, prosecutors said, quoting a recording of the alleged conversation.

Prosecutors alleged that at one point, Lee said the manual for making the pressure cooker bomb used in the Boston Marathon terror attack was available on the Internet, and that the bomb could be useful in times of war.

The lawmaker also allegedly made remarks sympathetic to North Korea and sang its military march songs before hundreds of members who attended the organization's meetings held between March and August of last year. Such acts are in violation of the anti-communist National Security Law, prosecutors added.

"The meeting on May 12 was a place to discuss what the UPP should do in case the United States launched an attack on North Korea, not in case of North Korea invading (South Korea)," Lee said.

Lee's lawyers argued that the prosecution had distorted the lawmaker's remarks, and that the recording cannot be submitted as evidence, as it was obtained through illegal means.

The court will hold hearings four times a week on average, and deliver a verdict sometime in January at the earliest, court officials said.

The court's ruling is likely to influence a decision by the Constitutional Court which is currently reviewing a petition filed the government calling for the disbandment of the UPP.

(Yonhap News)