"The Secretary-General condemns the killing of Mr. Zedi Feruzi, leader of the opposition Union pour la Paix et le Développement (UPD) Zigamibanga party in Burundi, and his bodyguard today in Bujumbura," the United Nations said in a statement published on its website on Saturday.
The assassinations, as well as the Friday grenade attack in Bujumbura's central market that killed two people, threatens to trigger more violence in Burundi, Ban Ki-moon stressed.
In late April, street protests erupted in Burundi following President Pierre Nkurunziza's announcement of his intention to run for a third term.
Opponents of the president deem this move unconstitutional, as the law requires him to step down after two terms.
In mid-May, Burundian authorities arrested two suspects for an attempted government coup.
The UN Secretary General stressed on Saturday that Burundian leaders must address the current political crisis in the country and to place national reconciliation above partisan interests.
