Government of Burundi have confirmed that President Pierre Nkurunziza has died of a heart attack.
In a statement posted on Twitter on Tuesday, the government announced "with great sorrow to Burundians and the international community" the passing of Nkurunziza, 55.
According to the statement, Nkurunziza had attended a volleyball match on Saturday afternoon and was taken to hospital that evening after falling ill.
Although he appeared to recover on Sunday and spoke to those around him, he suddenly deteriorated on Monday morning. He then suffered a heart attack and despite an immediate resuscitation attempt, doctors were unable to revive him.
Nkurunziza died at a hospital in Karuzi, eastern Burundi.
The government said there would be a period of national mourning for seven days from Tuesday and that flags would be flown at half-mast.
In power since 2005, Nkurunziza was due to be replaced in August by political ally Evariste Ndayishimiye, who was declared earlier this month the winner of a May 20 presidential election.
In 2015, the announcement that he would run for a third term plunged the country into chaos.
It sparked anger as some questioned the legality of a third-term bid.
There was a failed coup attempt, hundreds of people died in clashes and tens of thousands fled the country.
After a change in the constitution, he was able to run for a further term in last month's election but he decided to retire and was to be known as the "supreme guide to patriotism".