Tshisekedi won the Dec. 20-24 election by a landslide, but the vote was marred by widespread allegations of fraud, logistical shortcomings and disruptions.
The two opposition leaders, Martin Fayulu and Moise Katumbi, as well as others have called for a re-run - a demand authorities have dismissed.
"We are having a protest on Jan. 20 because we will not accept the results, there was fraud everywhere and the elections must be annulled," said Katumbi in an online press briefing.
(Reporting by Ange Kasongo and Sonia RolleyWriting by Nellie PeytonEditing by Andrew Heavens and Frances Kerry)
