Burundi's second vice president says he has fled the country fearing for his life after opposing the president's controversial bid for a third term that has sparked off violent protests in the capital in recent weeks.

Gervais Rufyikiri, believed to have taken refuge in Brussels last week, said in an interview on Radio France International aired Thursday that he has not officially resigned.

In a Twitter posting, the presidential adviser for information and media Willy Nyamitwe confirmed Rufyikiri had fled.

Rights activists say at least 77 people have died in streets protests against President Pierre Nkurunziza's bid for a third term in office in the July 15 presidential elections.

Critics say Nkurunziza's push for a third term violates the two-term limit for presidents set by the constitution.