The IFP's by-election victory in President Jacob Zuma's hometown of Nkandla was a significant milestone for the party, IFP leader Mangosuthu Buthelezi said on Saturday.
"...It seems everyone considers Nkandla the litmus test of President Jacob Zuma's leadership," Buthelezi said in a statement.
"And the test is showing high levels of acidity."
On Thursday the Independent Electoral Commission announced that the Inkatha Freedom Party won Ward four, in Nkandla, after the African National Congress councillor died of natural causes.
"When I travel outside KwaZulu Natal... and speak to people about the IFP's by-election victories in Mtubatuba, in Ulundi, Nongoma, Nqutu, Umtshezi and uPhongolo, there is an understanding that the IFP is gaining pace and support," Buthelezi said.
He said he was "thrilled" at the by-election results "because when I tell people the IFP won Nkandla, everyone smiles".
He attributed the win to his party's anti-corruption stance.
"The shadow of corruption has darkened the ANC's door to such an extent that the president's own people reject his party at the polls."
The IFP also won the Hlabisa ward, which was previously held jointly by the ANC and New Freedom Party.
Buthelezi took a swipe at Zanele KaMagwaza-Msibi, leader of break-away party the NFP.
"[KaMagwaza-Msibi] immediately complained that she knows her rivals import people into by-election wards to vote, which, ironically, is precisely what the NFP was exposed for doing in Nongoma three months ago."
Buthelezi predicted that the IFP would experience increased support in the near future.
"There is a groundswell of concerned South Africans looking to put their support in a party they can trust...That is the message coming out of one by-election after the next."