Bujumbura - Thousands of Burundian activists mourned a murdered opposition leader at his funeral Sunday, vowing to intensify their protests against a bid by the president of the central African nation to seek a third consecutive term.
Opposition leaders also said they were suspending talks with the government of President Pierre Nkurunziza after Zedi Feruzi, the leader of the Union for Peace and Development (UPD), a small opposition party, was gunned down in the capital on Saturday.
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"Those who killed Feruzi Zedi will pay sooner or later," one sign held by mourners read.
The killing came a day after a grenade attack on a busy market killed three people and injured around 40 others.
The attacks have dramatically worsened tensions in the crisis-hit country, where a heavy-handed crackdown on the anti-government demonstrations has already left around 30 dead since late April.
The crisis also sparked a failed coup against President Nkurunziza last week, and there are fears Burundi, which only emerged from a 13-year civil war in 2006, could be plunged back into conflict.
Condemning the apparent assassination as "an awful act", activists said in a statement they were "suspending participation in dialogue with the government" that had been supported by the United Nations and African Union.
They also said the murder could have been part of an alleged "plan to physically eliminate" leaders of the campaign against Nkurunziza. A journalist who witnessed the attack said the gunmen were clad in uniforms similar to those worn by the presidential guard.
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The presidency, however, said it was "shocked" by the attack, in which a police bodyguard was also killed, and called for the perpetrators to be found and brought to justice.
While the streets of the capital were calm Sunday in line with a weekend truce, protesters were readying to resume the demonstrations.
Civil society leader Pacifique Nininahazwe called the truce "to allow the people to bury with dignity those who died for democracy," but warned the "protests will resume on Monday with even more force".
UN appeals again for calm
The UN Secretary General Ban Ki-moon, who has already criticised Nkurunziza's attempt to stay in office, condemned the latest violence and appealed for "calm and restraint".
The European Union meanwhile called on the Burundian government to prosecute the perpetrators behind the attacks "and take the necessary steps to prevent the political violence from spreading".
Burundi's crisis, which began in late April after the ruling party nominated Nkurunziza to stand again in the June 26 presidential election, deepened last week when a top general staged a failed coup attempt.
Parliamentary polls, initially set for May 26, have been postponed to June 5.
Opposition and rights groups say that Nkurunziza's bid for a third five-year term violates the constitution and conditions of a peace deal that ended the civil war.
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Nkurunziza, a former rebel leader and born-again Christian who believes he has divine backing to lead the country, argues that his first term did not count as he was elected by parliament, not directly by the people.
Refugees continue to flee the violence, most of them to neighbouring Tanzania, where over 50,000 people are struggling to survive in dire conditions on the shores of Lake Tanganyika.
Cholera has broken out in squalid camps, where at least 31 people have died among a total of over 3 000 cases of the disease, and numbers are growing by up to 400 cases a day, according to the UN refugee agency.
"The situation is critical," Doctors Without Borders [MSF] officer Kassi Nanan N'Zeth said.
"The refugees are confronted with an impossible choice... stay in Burundi to face the insecurity, or to come to a Tanzanian refugee camp and face the possibility of cholera."