Bujumbura - Gunfire rang out in Burundi's capital on Sunday night following the killing of a feared military general who was a close ally of President Pierre Nkurunziza.
Nkurunziza, who was re-elected last month, said in a televised address that he had ordered the police to find Lieutenant General Adolphe Nshimirimana's killers within 10 days.
There is fear that the assassination of Nshimirimana could spark revenge killings and further fuel violence that stemmed from Nkurunziza's controversial bid for a third term.
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Carina Tertsakian of Human Rights Watch said Nshimirimana was "one of the key hardliners around the president" and was "generally seen as untouchable".
Nshimirimana is believed to have helped to defeat an attempted coup against Nkurunziza in May.
The US has condemned the killing and is urging restraint.