Gunmen in uniforms kill ally of Burundi's President Nkurunziza

Gunmen wearing military uniforms shot dead a former Burundian security chief who was a close ally of President Pierre Nkurunziza on Sunday, the presidency and witnesses said, heightening tensions after a disputed presidential poll.

General Adolphe Nshimirimana, who was in charge of the president's personal security at the time of his death, was killed in a car alongside three of his bodyguards in the Kamenge district of the capital Bujumbura, the sources said.

Witnesses said the four attackers wore military fatigues and sprayed the car with bullets, then drove off shortly after 8 am (0600 GMT). "Two had machine guns and two others rocket launchers. They came in military lorry and returned back in the same car," Paul, a taxi driver, said.

Pictures circulated via social media showed a black bullet-riddled SUV with its front tyres flattened and side windows shot out. "He has been killed by a bullet ... He was in the car with some bodyguards but I don't know exactly what happened," presidential adviser Willy Nyamitwe said. 

The army and police were unavailable for comment. Burundi has been in chaos since late April when Nkurunziza announced he would seek a third term in office, a move Western powers and opponents said violated the constitution and a peace deal that ended an ethnically-charged civil war in 2005.

Months of protests and a coup attempt were quelled, but the capital and some areas in the countryside have been rocked by sporadic violence and killings. Some of the army generals behind the attempted coup have vowed to lead a rebellion to oust Nkurunziza, who won the July 21 presidential poll after the opposition boycotted the elections.

African leaders fear the violence could split the country down ethnic lines and lead to another civil war, an alarming prospect for a region still scared by the 1994 genocide in neighbouring Rwanda where 800,000 Tutsi and moderate Hutus were slaughtered. Burundi has a similar ethnic make-up.

Western diplomats have also warned a rift in the army could push Burundi back into conflict. The last 12-year civil war pitted the military, which at the time was led by the ethnic Tutsi minority, against rebel factions of the majority Hutus, the biggest of which was led by Nkurunziza.