Prosecutors investigating election meddling allegations have again summoned the chief of staff for former Ulsan mayor Kim Gi-hyeon for questioning.

On Thursday, Park Ki-seong was questioned over details on how Ulsan City Hall employees leaked information to the city's former vice mayor Song Byung-gi, including what was leaked and why.

The grilling took place at the Ulsan District Prosecutors Office as prosecutors and investigators have been dispatched from Seoul to Ulsan to probe the case.

Prosecutors are known to have confirmed through Park the names of four to five former and incumbent civil servants who leaked internal materials to the ex-vice mayor and whether this had an impact on the provincial elections.

Song was at the time working for the election campaign of current Ulsan mayor Song Cheol-ho who was running as a candidate. The prosecution believes the information was used to help build election pledges to beat his rival Kim Gi-hyeon.