A North Korean propaganda outlet on Wednesday criticized South Korea's recent mayoral elections as an example of "backward" politics, saying the races were marred by mudslinging and negative campaigning.

Last week's mayoral by-elections in Seoul and the southeastern city of Busan ended with the ruling Democratic Party's crushing defeat after the campaigns were dominated by alleged real estate speculation and criticism of the Moon Jae-in administration's real estate policy.

Tongil Voice, a North Korean propaganda radio broadcast, slammed the elections as a "rampage of madmen crazy for power" and criticized the mayoral candidates for defaming each other with words like "trash" and "severe dementia." 

"The by-elections show that so-called politics in South Korea are not aimed at advancing society but rather bring regression that runs counter to public sentiment and creates confusion," it said.

The outlet accused Oh Se-hoon, the main opposition People Power Party (PPP) candidate in Seoul, and Ahn Cheol-soo of the minor opposition People's Party of pointing "swords at each other" after forging an alliance.

Oh was chosen to become the single opposition candidate after the two had sought to merge their campaigns in a bid to raise chances of election victory for the broader opposition bloc.

Oh won the election and took office as Seoul's mayor on Thursday. (Yonhap)