Democratic Republic of Congo's elections to replace President Joseph Kabila, who has been in power for nearly 18 years, will be indefinitely delayed despite already being more than two years behind schedule, said one of the candidates Thursday.

One of the  21 candidates for president , Noel Tshiani who was called to a meeting by the head of Congo's electoral commission, said they were told that Sunday's long-promised vote could not be held on time because of technical problems, a fire that incinerated thousands of voting machines last week and an intensifying Ebola outbreak in the country's restive east.

Kabila's chosen successor, Emmanuel Ramazani Shadary, is facing off primarily against two other candidates - Felix Tshisekedi, the son of Congo's veteran opposition leader who died earlier this year, and Martin Fayulu, a former Exxon executive who is backed by two political heavyweights who were barred from candidacy.

In an interview with The Washington Post last week, Kabila had expressed certainty that the election would be held on time. Its delay casts a pall of doubt over its eventual integrity, which has already been marred by widespread political violence and a ban on campaigning in the capital Kinshasa.

Congo is sub-Saharan Africa's biggest country by area and its more than 80 million people have never experienced a peaceful, democratic transfer of power.

The country has been a source of regional instability for decades and more than a hundred armed groups operate through its territory.