The party expressed concern that the development was an indication of what to expect in 2019.
In statement signed by National Publicity Secretary Yemi Kolapo, the party said: “It is now clear that the failed All Progressives Congress government will stop at nothing to subvert the people’s will.
“At the main elections a week ago, the people of Osun had delivered a most damning verdict on the Rauf Aregbesola-led APC but the APC has exposed its own disdain for democratic tenets by its shameful conduct at Thursday’s rerun.
“The most tragic aspect of the entire charade was the odious role played by the police in sabotaging the entire process, with its conspiracy with the APC to prevent opposition supporters from voting.
“The same policemen engaged in indiscriminate arrests of election observers and journalists duly accredited to cover the polls. There were ‘parades’ by policemen on the streets of Oshogbo who fired gunshots sporadically to scare voters.
Even the Independent National Electoral Commission has distanced itself from the conduct of the police.
“If the President of the Federal Republic of Nigeria could come out to congratulate a winner in this kind of election, then his integrity is seriously at stake.
While we reject the outcome of the Osun fiasco in its entirety, we urge all Nigerians to stand firm and ensure that this does not happen again.