Bujumbura has been rocked by six consecutive days of demonstrations against President Pierre Nkurunziza, who on Friday warned of "severe sanctions" against those protesting over his decision to seek a third term in office.
The protests have sparked the biggest political crisis since an ethnically fueled civil war ended in 2005. The presidency has called the demonstrations an "insurrection".
Opponents say Nkurunziza is violating the constitution and the Arusha peace deal by seeking a third five-year mandate at elections on June 26.
Pre-vote fears have driven more than 26,000 Burundians to neighboring Congo and Rwanda, officials say.
The United Nations, which has voiced concerns intelligence and security services are using live ammunition at protests, said there are "credible" reports of detained protesters being beaten and held in overcrowded conditions.
Nkurunziza`s supporters say he can run again because his first term, when he was picked by lawmakers and not elected, does not count. The United States, however, disagrees and has said his candidacy is a violation of the Arusha accords.
The crisis is being closely watched in a region still scarred by the 1994 genocide that killed more than 800,000 people in neighboring Rwanda which, like Burundi, is divided between ethnic Tutsis and Hutus.
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