Nkurunziza made the decision after a recommendation by the election commission and following requests from opposition politicians and the international community for a postponement, Willy Nyamitwe told Reuters on Wednesday.
Following a now daily pattern of street protests against Nkurunziza, demonstrators gathered in the capital shortly after dawn to chant slogans calling for the 51-year-old former sports professor not to seek a third term in office.
Police fired tear gas at one group of demonstrators, and a few shots were heard, a Reuters’ photographer said.
The protesters say Nkurunziza's desire to extend his time in office violates the constitution and a peace accord that ended an ethnically charged civil war in 2005. As many as 300,000 people died in the conflict.
Regional heavyweight South Africa called this week for the June 26 presidential election to be postponed indefinitely to allow stability to return.
However, diplomats fear that the longer the crisis drags on, the greater the chance that what is essentially a power struggle could re-open old wounds in a country with a long history of mass ethnic killing between its Hutu majority and Tutsi minority.
A failed coup last week appeared to expose rifts in the military, a key pillar of post-war unity and reconciliation. Nyamitwe denied any splits in the security forces.
"The army is not divided," he told Reuters.
Nkurunziza argues that his presidential bid is legitimate since he was appointed to his first term in office by parliament, rather than by a direct vote.