Human Rights Watch is calling for political candidates in the Democratic Republic of Congo to refrain from inciting violence during the country's election campaign, which begins Friday.

The international human rights watchdog says it has documented dozens of recent instances in which candidates used “apparent ethnic hate speech” in order to incite violence, primarily against opposition candidates and their supporters.

The group says police have used excessive force against opposition demonstrators, raising concerns about the credibility of the November 28 presidential and parliamentary elections.

President Joseph Kabila is facing a divided opposition in the presidential election. One of his strongest challengers is Etienne Tshisekedi, a 78-year-old veteran politician who boycotted the 2006 presidential race.

Human Rights Watch says politicians and supporters of parties aligned with President Kabila have referred to supporters of Mr. Tshisekedi as mosquitoes that need to be exterminated.

The Carter Center, a widely respected election monitoring group, also says the election faces “serious” credibility threats, saying it has received reports of intimidation and violence at campaign events.

Earlier this month, President Kabila expressed confidence that he will win re-election.

Mr. Kabila promised to step down if he is defeated, but said “I know one thing for sure, I will not lose.”