Burundi’s government says President Pierre Nkurunziza has died of a heart attack at age 55.

A statement says the president was admitted to a hospital overnight Saturday after not feeling well. He appeared better Sunday but “to very great surprise” his health abruptly worsened Monday morning, and several hours of effort failed to revive him.

Nkurunziza took office 15 years ago, and his decision to run for a disputed third term in 2015 led Burundi into turmoil that left hundreds of people dead. Facing allegations of widespread abuses, his government angrily rejected scrutiny, becoming the first country to leave the International Criminal Court.

His death comes on the heels of elections on May 20 in which his hand-picked successor, Evariste Ndayishimiye, secured a seven-year term as president — a result confirmed by the constitutional court last Thursday.

Ndayishimiye was due to be sworn in in August.

The statement from Burundi’s presidency on Tuesday the country would observe seven days of mourning beginning Tuesday.

(FRANCE 24 with AFP)