Burundi's President Pierre Nkurunziza has won a third term in office, an electoral official announced Friday, amid unrest over whether his third term is constitutional.

Nkurunziza won 69 percent of the vote while his closest rival, Agathon Rwasa, got 19 percent, said electoral chief Pierre-Claver Ndayicariye.

Nkurunziza, 51, was expected to win because he did not face a strong challenge in Tuesday's polls after some opposition groups boycotted the election. Rwasa, the leading opposition candidate, said his campaign had been hindered by officials.

The United States and Britain have condemned the elections as not being credible because of violence, intimidation of opposition groups, the government shutting down independent media and questions over the constitutionality of Nkurunziza's bid for a third term.