Burundi has appointed a new vice-president - Frederic Ngenzebuhoro of the Uprona - the main Tutsi party.
The referendum on the constitution has been delayed
The move fulfils a pledge by President Domitien Ndayizeye - who is a Hutu - that his deputy would be a Tutsi.
The president dismissed his Tutsi former vice-president, Alphonse Kadege, accusing him of undermining efforts to end the country's 11-year civil war.
Mr Kadege had repeatedly said a draft constitution gives too much power to the country's Hutu majority.
A referendum on the draft has been delayed until 26 November after the timetable slipped due to disputes over power sharing.
Under a power-sharing deal signed in August, the Tutsi minority will have 40% of government and national assembly posts, compared to 60% for Hutus.
This is the basis for the new constitution, which needs to be passed by referendum before election local and legislative elections in March and presidential elections in April.
Campaigning to encourage voters to support the new constitution got underway on Friday with an open-air rally in the central town of Gitega.
Mr Ngenzebuhoro, 52, held several ministerial positions under former Tutsi President Pierre Buyoya.
Some 300,000 people have been killed since the civil war broke out in 1993.
About 5,000 United Nations peacekeepers are in the country to support the South African-brokered peace process.