KINSHASA (Reuters) - Former Democratic Republic of Congo President Joseph Kabila’s anti-corruption czar withdrew his candidacy from next month’s senate election due to what he said was widespread vote-buying.

Luzolo Bambi is at least the fourth candidate to drop out of the campaign after making such allegations against provincial assembly members, who vote for senators in indirect elections. No one, however, has named specific offenders.

President Felix Tshisekedi, who succeeded Kabila last month after a disputed election that the runner-up said was rigged, has promised to make the fight against corruption a cornerstone of his administration and condemned the reports of vote-buying.

In a letter to Congo’s electoral commission president dated Feb. 22 and seen by Reuters on Wednesday, Bambi, a special advisor to Kabila on graft and money laundering, withdrew his candidacy for the March 6 election.

“Having assessed and witnessed votes being sold during this election, I prefer to safeguard my values ... in order to preserve my honour, which has no price,” he wrote to commission president Corneille Nangaa.

Bambi said in a second letter addressed to Congo’s top prosecutor last week that he had collected evidence about “general corruption” in the senate and governor’s elections the same day and called for an investigation.

Tshisekedi allies Vidiye Tshimanga and Adam Bombole and a member of Kabila’s coalition, Jolie Kenda, have also dropped out of senate races, saying they were asked to pay bribes of as much as $50,0000.

Bambi estimated in 2015 that Congo loses up to $15 billion a year, about twice the country’s annual budget, to fraud, but prosecutions of high-ranking officials have been rare.

Speaking to reporters on Tuesday, Tshisekedi condemned the reported corruption and said he intends to rethink the indirect system by which senators and governors are elected.

“We will not be able to eradicate corruption by the simple fact of being in power as this phenomenon has been ingrained in the Congolese habits and traditions for many decades,” he said.

Nangaa was among five senior Congolese officials accused by the United States of “significant corruption relating to the (presidential) electoral process”. Washington imposed travel restrictions on the five last week.

Nangaa denied the accusations and told Reuters: “I don’t need to travel to the U.S., so the ban does not affect me.”

Congolese sources in contact with Nangaa and other senior government officials told Reuters that another candidate actually won the election but top officials instructed the commission to award the vote to Tshisekedi.