Ukraine's interior minister has accused the incumbent president and a former premier of waging campaigns that involve bribing voters ahead of Sunday's presidential vote.

In a statement issued late Thursday, Arsen Avakov said that his ministry is looking into hundreds of claims that campaigners for President Petro Poroshenko and former Prime Minister Yulia Tymoshenko were offering money to voters who would promise to cast a ballot for their candidate.

He noted that about 60 percent of complaints about bribes refer to Poroshenko's campaign, and Tymoshenko's campaign accounts for the rest. Both campaigns have repeatedly denied the accusations.

Opinion polls show Poroshenko and Tymoshenko trailing comedian Volodymyr Zelenskiy, who stars in a TV series about a teacher who becomes president after a video of him denouncing corruption goes viral.