The leader of a small Burundian opposition party was shot dead on Saturday, residents said, the latest violence in a country gripped by weeks of protests over the president's controversial bid to seek a third term.
Zedi Feruzi, the head of the Union for Peace and Development (UPD) was walking home under police protection in Bujumbura's Ngagara District when he came under fire, locals told AFP, adding that one of the three officers accompanying him was also killed in the incident.
The unknown gunmen were able to flee the scene in a car.
An AFP reporter saw the bloodied bodies of both Feruzi and a police bodyguard lying outside the house soon after the shooting.
The attack — which comes a day after a grenade attack on a busy market killed three people and injured around 40 others — risks further fuelling tensions in the capital where a heavy-handed crackdown on anti-government demos has left more than 20 people dead since late April.
The crisis also sparked a failed coup against President Pierre Nkurunziza last week.
Saturday's shooting brought a dramatic end to what had been a rare day of calm in the city after protest leaders called for a pause in the demos to allow people to stock up on supplies and bury their dead.
"We heard around 20 gunshots, everyone fell to the ground, people saw a Toyota car speeding away," said a resident in the Ngagara District, who did not himself witness Feruzi's shooting.
A police officer who was among those tasked with protecting Feruzi was seriously injured in the hail of bullets.
"We were returning on foot when a Toyota IT pulled up alongside us and the men inside opened fire on us," the officer, who did not give his name, told AFP from his hospital bed. "I fell, I don't know what happened after that."
Radio journalist Jean-Baptiste Bireha said he was talking with Feruzi at the precise moment when the attackers appeared and started firing.
He said the gunmen were clad in uniforms similar to those worn by the presidential guard.
"When they left, they were shouting and singing, they threw some grenades to scare us," said Bireha, who was unharmed.
But the presidency denied any involvement, saying it was "shocked" by the killings which it said should be urgently investigated "so the guilty are brought to justice".
In the wake of the shooting local youths sealed off streets and alleyways to outsiders, while two barricades of tyres were set alight in the district.
The attack signals another escalation in violence in Bujumbura after the attack on the market Friday.
Police have said they are questioning a suspect in the grenade attack, which they blamed on the anti-government demonstrators.
But civil society leader Vital Nshimirimana, a key organiser of the protests, dismissed the accusation, and called for the international community to investigate.
"We have obviously nothing to do with these grenade attacks," Nshimirimana said.
"Police are trying to demonise us to justify the fact that they shot and killed unarmed demonstrators."
Meanwhile another civil society leader, Pacifique Nininahazwe, on Friday announced a weekend truce "to allow the people to bury with dignity those who died for democracy."
But he warned that "protests will resume on Monday with even more force."
In a small sign of progress, he added that discreet talks had begun this week between the protesters, opposition parties and the government.
The negotiations have been supported by the United Nations, African Union and regional nations.
Burundi's crisis, which began in late April after the ruling party nominated Nkurunziza to stand again in the June 26 presidential election, deepened last week when a top general staged a failed coup attempt.
Parliamentary polls, initially set for May 26, have been postponed to June 5.
Opposition and rights groups say that Nkurunziza's bid for a third five-year term violates the constitution and conditions of a peace deal that ended a 13-year civil war in 2006.
Nkurunziza, a former rebel leader and born-again Christian who believes he has divine backing to lead the country, argues that his first term did not count as he was elected by parliament, not directly by the people.
Refugees continue to flee the violence, most of them to neighbouring Tanzania, where over 50,000 people are struggling to survive in dire conditions on the shores of Lake Tanganyika.
Cholera has broken out in squalid camps there, with at least 31 people having died among a total of over 3,000 cases of the disease, with numbers growing by up to 400 cases a day, according to the UN refugee agency.