Zedi Feruzi, the head of Burundi opposition party UPD was Saturday shot dead in the capital Bujumbura.
Feruzi was killed along with his bodyguard in the Ngagara district.
Anshere Nikoyagize, the head of the civil society group Ligue ITEKA, told Reuters that Feruzi was killed near his home.
Protests against President Pierre Nkurunziza’s bid for a third term have persisted in the capital with civilians clashing with police.
Feruzi was among opposition figures and activists who are condemning Nkurunziza’s decision to breach the constitution and the Arusha accord that ended an ethnically fuelled civil war in 2005.
“We heard a lot of gunfire,” a neighbor of Feruzi told Reuters Television saying army men were on the scene but did nothing.
Feruzi, a member of the African nation’s relatively small Muslim community, was a well-known figure although his party was not among the nation’s biggest.
He was shot in the head dying instantly.
After his killing, Ngagara residents set up barricades on the streets with police firing teargas and water cannons and residents responding with stones.
Activists suspend talks with government
Burundi opposition has vowed to keep on protesting until Nkurunziza ends his re-election bid.
Activists behind weeks of protests against said Sunday they were suspending talks with the government after the murder of an opposition figure.
Condemning “an awful act”, activists said in a statement they were “suspending participation in dialogue with the government” after the assassination of Feruzi.
Two people were also killed when three grenades went off in a market in the Burundi capital on Friday.
At least nine people were wounded in the incident.
US suspends military aid
The United States said on Friday it had suspended training of Burundi soldiers for African peacekeeping missions over concerns that political violence in the country would hamper their ability to participate in such operations.
“The U.S. has temporarily halted peacekeeping training activities such as the Africa Contingency Operations Training and Assistance program,” State Department spokeswoman Marie Harf told a daily briefing.
“Continued instability and violence in Burundi, and in particular the commission of human rights violations and abuses by security forces, could jeopardize Burundi’s ability to continue to contribute to the AMISOM peacekeeping mission,” she added.
Harf said, however, that Burundi’s military has largely acted “professionally and neutrally” during the protest, and some had lost their lives.
According to the White House, since 2005 through the Africa Contingency Operations Training and Assistance (ACOTA) program, the United States has trained more than 248,000 peacekeepers from 25 countries in Africa before they are deployed for U.N. and African Union peacekeeping operations.
Washington has expended more than $241 million in ACOTA activities since 2009 alone, the White House said.