Two prominent opposition leaders in Burundi have said they will boycott presidential elections in June unless President Pierre Nkurunziza drops his bid to stand for a third term.
Aspiring presidential candidates Agathon Rwasa and Jean Minani said on Thursday that the elections would not be free and fair if Nkurunziza was allowed to stand.
Rwasa told Al Jazeera that credible elections could not take place while the current political crisis was ongoing.
"When the constitution is thrown away, is there any room for a democratic election?" he said.
On Wednesday, a constitutional court said it would examine the legality of Nkurunziza's bid for a third term.
"Nkurunziza believes in weapons and militiamen...he prefers to spur violence not knowing he risks leaving office prematurely," Rwasa added.
Minani, the leader of the Front for Democracy in Burundi, and Rwasa, a former rebel with the National Liberation Forces, both command huge sway in the country.
The warnings to boycott, made separately by the pair, came as protests continued into their fifth day in the capital, with protesters vowing not to leave the streets until Nkurunziza withdrew his candidacy for the coming vote.
At least six people have been killed in the violence, according to the Red Cross.
Al Jazeera's Malcolm Webb, reporting from Burundi's capital Bujumbura, said tensions were high in the capital, with radio stations supportive of the ruling party broadcasting tracts evocative of ethnic conflicts the country has previously experienced.
"They're not openly calling for attack, however, they are talking extensively about ethnic conflicts the region has experienced... past violence dating back to the seventies," Webb said.
"The current conflict is not ethnic, it's a political contest with Tutsis and Hutus on both sides, not a competition for power based on ethnic lines."
Meanwhile, the US warned Burundi it had "serious concerns" about the ongoing political violence in the country.
The Reuters news agency said an unnamed US diplomat had urged Nkurunziza to allow space for peaceful protest, and for the media to maintain strong relations with the international community.
Nkurunziza had in turn told the diplomat that the protests in the capital were "illegal", but said there would be no restrictions on the opposition.
Source: Al Jazeera And Agencies