Addressing supporters in his hometown in the north of the country yesterday, Nkurunziza thanked those who backed him after a top general launched a failed coup while the president was out of the country in May for a summit.
He "warned any person who tries to take power by overthrowing elected institutions", saying "any such attempt will go nowhere", a statement from the ruling CNDD-FDD party said.
The crisis in Burundi erupted in late April after the ruling party designated Nkurunziza, in power for 10 years, as its candidate in upcoming elections. Weeks of street protests, which were brutally suppressed, left at least 30 dead.
The opposition and rights groups say the president's third-term bid violates a constitutional two-term limit as well as a 2006 peace deal that ended a 13-year civil war.
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Nkurunziza, a former rebel leader from the Hutu majority and a born-again Christian, insists he has every right to stand again because he was elected to his first term by parliament, not directly by the people.
Yesterday, regional leaders called for the polls to be delayed by at least a month and a half but stopped short of telling the president to abandon his re-election campaign.
Government spokesman Philippe Nzobonariba told AFP that the government welcomed the proposal to delay the polls, adding that his third-term bid was a sovereign issue and that the government now considered the matter "closed".
Plans by the government to push ahead with the polls have been hit by a string of setbacks, with the influential Catholic Church withdrawing its support and key international donors also suspending crucial aid.
The election panel has now been left with just three sitting members, effectively stripping it of its ability to take decisions -- which normally have to be taken after the agreement of four of its members.