"Investigations into the Lee administration that the ruling bloc has encouraged the prosecution to conduct are only a show of political retribution for Roh's death," Hong wrote on Facebook.

"This amounts to a denial of the country's modern history that preceded the left-wing government, whose remaining term is just less than five years," he added.

The ruling camp has pushed for the investigations, with the goal of shoring up social justice and democracy, institutions which are thought to have been eroded by the alleged wrongdoings of the Lee and Park Geun-hye administrations.

The probes have faced intense resistance from conservatives who argue that they will only deepen national division and complicate efforts to tackle the security and economic challenges facing the country.

In a tit-for-tat move, the LKP has called for an independent counsel to probe the long-forgotten graft scandal involving Roh.

The escalating standoff spells trouble ahead for the ruling Democratic Party and the government, who have been seeking opposition support for a series of bills necessary to advance Moon's reform agenda, such as overhauling the prosecution and spy agency.

Further aggravating political tensions, the ruling party raised fresh suspicions Thursday that the Lee administration conducted illicit surveillance on liberal mayors and governors, and interfered in elections and the personnel affairs of local broadcaster KBS. 

Unfazed by the pushback, Choo Mi-ae, the ruling party leader, called for a "thorough" investigation into the alleged wrongdoings of the past governments.

"The law enforcement authorities must verify how state power undermined the democratic, constitutional order and they must ensure that this will never occur again," she said during a party meeting. (Yonhap)