Song, who ran as the ruling Democratic Party candidate, pushed to build a hospital for the public, while his rival Kim Gi-hyeon, the then-mayor who ran as the main opposition Liberty Korea Party candidate, pledged to build a hospital specializing in labor accidents.

The latter plan, considered a long-term goal for the city known for its industrial plants, fell through as a preliminary government review concluded that it was infeasible. The decision came on May 28, just 16 days ahead of the June 13 elections.

Prosecutors are known to have secured evidence -- a note belonging to current Ulsan Vice Mayor Song Byeong-gi -- that indicates the two Songs exchanged opinions on the public hospital issue with Cheong Wa Dae from 2017.

The Friday raid comes just two days after investigators searched the workspace of an official at the prime minister's office who is allegedly involved in the election-meddling case.

The official previously worked at Cheong Wa Dae's civil affairs unit, where he allegedly compiled documents on bribery allegations of former mayor Kim's confidants in October 2017 based on tips from Ulsan Vice Mayor Song.

The election-meddling allegations blew up into a massive investigation after former mayor Kim claimed that the Ulsan Metropolitan Police Agency deliberately raided his office a few months ahead of the election with the presidential office behind the move.

Kim claimed that some presidential officials allegedly compiled a document on bribery allegations involving his confidants based on tips from Vice Mayor Song, which led to the raid that negatively affected his election campaign.

In a press briefing held Friday, Kim accused Cheong Wa Dae and the finance ministry of intervening in the mayoral race.

Kim claimed the process and result of the preliminary government review of the hospital project was "very contrived."

"(Vice Mayor) Song's note shows they had an internal strategy to fail the (plan on building the) hospital specializing in labor accidents," Kim said. "The nature of the crime, in which Cheong Wa Dae and a government ministry moved according to the strategy, is very bad."

The presidential office, which underwent a court-issued search earlier this month, has flatly denied all allegations linked to the election-meddling case.

The finance ministry also argued there were no political motives throughout the review process.

"After (the hospital project) was selected (to undergo) a preliminary feasibility study in November 2013, (the process) took longer than other projects, as the labor ministry and the city of Ulsan changed the project plan several times," a ministry official said.

"It is understood there was not much additional benefit (from the hospital project) as there are many major hospitals in Ulsan.

Political scheduling was not considered at all at the time of the (study result) announcement." (Yonhap)