Congo's opposition candidate for president has spoken out for the first time since leaving the country in May for medical reasons, criticizing President Joseph Kabila for not reassuring the public that elections will take place on time.

Moise Katumbi late Thursday said a united opposition will ensure a peaceful and transparent transition of power.

Authorities in Congo last month sentenced Katumbi to three years in prison in absentia relating to allegations that he falsely acquired a building. Katumbi's supporters call it a political move aimed at stopping him from running in the presidential election.

Katumbi said "neither false convictions, nor harassment, nor physical abuse will shake my determination."

The opposition has expressed concern that the election set for November will be delayed so that Kabila will stay in power longer.