The National Intelligence Service is expanding its investigation into the Unified Progressive Party, looking into possible connections two of its lawmakers may have to an underground organization suspected of plotting a pro-North Korea rebellion.

The NIS arrested Rep. Lee Seok-ki and other leading members of the left-wing party last week.

The agency has launched an inquiry into UPP Reps. Kim Mi-hyui and Kim Jae-yeon and others believed to be members of the Revolutionary Organization allegedly led by Lee.

Lee is accused of forming RO within the East Gyeonggi Coalition and of instructing its members to secure firearms and make plans to assist North Korea in the event of an inter-Korean war.

Since Lee was taken into custody, reports have emerged that Kim Mi-hyui is a high-level member of the RO, and that she had been in contact with the organization’s Pyongyang connection.

By Choi He-suk  (cheesuk@heraldcorp.com)