There were celebrations in the streets of Bujumbura on 13 May after a Burundi army general said he had sacked Pierre Nkurunziza as president for seeking an unconstitutional third term in office, and was working with civil society groups to form a transitional government.

The presidential office quickly rubbished the declaration by General Godefroid Niyombareh, who was fired by Nkurunziza as intelligence chief in February. "We consider it as a joke not as a military coup," presidential aide Willy Niyamitwe said.

But crowds of people streamed on to the streets of Burundi's capital, cheering and singing, after the announcement and soldiers surrounded the state broadcaster building.

Niyombareh made his declaration to reporters at a military barracks in Bujumbura, while the president was out of the country at an African summit on the crisis.

More than 20 people have been killed since street protests erupted in the impoverished central African state more than two weeks ago, according to an unofficial count by activists.

The demonstrators say Nkurunziza's bid for another five years in office violates a two-term limit in the constitution and the Arusha peace deal, which ended an ethnically fuelled civil war in 2005 that killed 300,000 people.

East African leaders and a top official from continental heavyweight South Africa were meeting in Tanzania's commercial capital Dar es Salaam to discuss the crisis that has already spilled over into a region with a history of ethnic conflict.

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