BUJUMBURA, Burundi — Burundi’s voters approved a new Constitution that extends the presidential term from five to seven years, according to provisional figures released on Friday, handing a major victory to President Pierre Nkurunziza.

Mr. Nkurunziza, who beat a two-term limit under the old Constitution through an electoral technicality to take a third term as president, is widely expected to run again, in 2020.

The outcome “opens a chapter of harsh dictatorship, where the president will be beyond any other institution,” Agathon Rwasa, who led the campaign against the new Constitution, said ahead of the provisional results.

Government officials, on the other hand, characterized the new Constitution as an emblem of national sovereignty and a path to a more efficient government.