Burundi president Pierre Nkurunziza has died aged 56 as a result of a heart attack, AP reported referring to the government's statement.

According to it, the president was hospitalized on Saturday night. His condition worsened sharply on Monday morning.

Nkurunziza took office 15 years ago, and his decision to run for a controversial third term in 2015 led to unrest, resulting in hundreds of deaths.

He passed away a few weeks before the candidate from the ruling party, Evariste Ndayishimiye, was to be sworn in after winning the May election.

The Government of Burundi has declared a week of mourning.