Kim said that an Ahn administration would seek a constitutional revision in 2018 and pave the way for the launch of a new government in 2020 based on the revision -- a pledge that hints that if Ahn is elected in the May 9 vote, the five-year presidential term will be truncated.

"In line with Ahn's request that I spearhead the panel to prepare for a joint government tasked with national integration and reform, (I) will run the panel from today onwards," Kim told reporters.

"When the revision will be applied is a decision for the National Assembly to make ... but I think Ahn's pledge is that if the Assembly decides to launch a new government when the next Assembly term begins in 2020, Ahn will follow that decision," he added.

Kim bolted from the Democratic Party in March after a conflict with the party's current presidential candidate Moon Jae-in.

Ahn has brought in Kim to his campaign as he has been struggling to boost voter support. He has seen his ratings fall due in part to his lackluster performances during a recent series of televised presidential debates.

In the latest survey announced Sunday by local pollster Realmeter, runner-up Ahn's support fell 1.9 percentage points to 20.9 percent, while frontrunner Moon has maintained a comfortable lead with 42.6 percent.

During the press conference, Kim said that Ahn's joint government will join forces with all reformist groups except for those who are "hegemonic forces" -- an apparent allusion to Moon who has formed a large powerful faction within his party.

"The joint reformist government will quickly complete all measures to reform political, economical and social sectors," he added.

Asked if the envisioned government can join hands with Hong Joon-pyo, the presidential candidate of the conservative Liberty Korea Party, Kim said that it will cover political forces regardless of their ideological orientations.

Hong's campaign, however, said that Ahn's plan for a "joint" government as a "makeshift measure" to court conservative voters.

"Ahn and we have different blood types ... The moment we do the blood transfusion, we will die," a Liberty Korea Party official told Yonhap News Agency, declining to be named. (Yonhap)