Security advisor to Burundi’s vice-president, General Athanase Kararuza has been shot dead while dropping off his daughter at school in the capital Bujumbura, BBC reports.
General Athanase Kararuza and his wife died instantly. No group has claimed the responsibility.
More than 400 people have been killed in the turmoil since President Pierre Nkurunziza said he would run for a third term last April.
A string of high-ranking army officials have been targeted during the conflict.
Security forces have also been accused of killing opponents and dumping them in mass graves by rights group Amnesty International.
Shortly after the attack, the International Criminal court announced that it was starting a preliminary investigation into the violence in Burundi.
This will decide whether a full-blown investigation will take place, which could result in charges against those accused of being behind the violence.
BBC reported that the killing is a blow for President Nkurunziza because it shows that he cannot guarantee the safety of his officers.
On Sunday the Minister for Human Rights Martin Nivyabandi survived a grenade attack as he was coming out of church.
Although both opposition and government forces are ethnically mixed, some fear that the violence could descend into a repeat of the genocidal killings which the country has previously experienced.
President Nkurunziza is the former leader of a Hutu rebel group which battled a Tutsi-dominated army for many years until he came to power in 2005 as part of a peace deal.
The African Union had said it would send a 5,000-strong peacekeeping force to the country even if the government did not accept it but it has since back-tracked.