The commission's president, Corneille Nangaa, said counting centres were still waiting for more than 80% of voting tallies to be submitted by local polling stations.

He did not say what had caused the delays, but opposition candidates seized on his statement to repeat their allegations of electoral fraud.

Regional monitors - from the African Union and the Southern African Development Community - have described last Sunday's election as "reasonably well-managed".

But the Roman Catholic Church's observer team reported more than 100 cases of election monitors being denied access to polling stations.

It added that around 20% of polling stations opened late, and there were reports of polling stations being moved at the last minute.

Another local observer group, Symocel, said some of its 20,000 agents were subjected to intimidation.

Some 1.26 million out of an electorate of nearly 40 million were excluded from Sunday's vote.

They are voters in the cities of Béni, Butembo and Yumbi who have had their vote delayed until March, well after the new president will be inaugurated in January.

The electoral commission said the deadly Ebola outbreak and insecurity made it impossible.