A minor opposition lawmaker suspected by the state intelligence agency of plotting a rebellion against the state claimed Thursday that the allegations had been fabricated in an effort to suppress democratic forces.

The National Intelligence Service raided the homes and offices of Rep. Lee Seok-ki and nine other members of the minor opposition Unified Progressive Party (UPP) on Wednesday for allegedly plotting a rebellion involving blowing up infrastructure in the country and helping North Korea in the event of an inter-Korean war.

Three of the party members were arrested in connection with the case.

"All the charges against me are a fabrication," Lee said at a party meeting at the National Assembly. "This is a tremendous repression scheme that is unprecedented since the beginning of history."

It was the first time that Lee had appeared in public since the spy agency began its raid, which is set to resume later in the day.

Wednesday's raid lasted more than 16 hours as NIS agents gathered relevant materials from Lee's office.

The UPP denounced the raid as a suppression of democracy and a return to the authoritarian regime of late strongman Park Chung-hee -- the father of incumbent President Park Geun-hye -- who ruled the country for 18 years until his assassination in 1979.

"Cheong Wa Dae and the NIS have set up a bizarre fabrication against our party," the UPP said in a statement released shortly after the meeting. Cheong Wa Dae is the name of South Korea's presidential office.

"The NIS investigation targets Rep. Lee so as to isolate and destroy progressive forces and break up the UPP," the statement said. "(It is) a crackdown aimed at making people tremble with fear and blowing out the candles."

In recent months, various liberal civic groups have held candlelight rallies in the center of Seoul to demand an apology from Park over allegations that the NIS conducted an online smear campaign against the opposition candidate to help her win last year's presidential election.

The UPP vowed to mobilize all of its local and regional chapters to fight the alleged suppression.

Rep. Choi Kyoung-hwan, the floor leader of the ruling Saenuri Party, called for a strict investigation into the case.

"If (Lee) has a clear conscience, all he has to do is cooperate with the investigation and prove his innocence," Choi said in a phone interview with Yonhap News Agency. (Yonhap News)