Burundi's outgoing president, Pierre Nkurunziza, died unexpectedly on Monday just weeks after his handpicked successor was elected to office in a poll marred by voter fraud allegations and arrests of opposition supporters.

With his election victory last month, Evariste Ndayishimiye had already become Burundi's president-elect, but the expectation was that Nkurunziza would be the power behind the throne - a strategy adopted by former president Joseph Kabila in the neighbouring Democratic Republic of Congo.

Burundi is run by a cohort of former fighters from the country's 13-year civil war, and Ndayishimiye "is cut from the same cloth", said Richard Moncrieff, project director for Central Africa at the International Crisis Group.

If there is a risk, according to Moncrieff, it is in the "destabalisation of the networks of power" in the country following Nkurunziza's demise.

Last week, the constitutional court rejected opposition leader Agathon Rwasa's allegations of voter fraud - so there is now a clear constitutional path for Ndayishimiye to be sworn in at the end of August for a seven-year term.