The Burundian opposition leader, Agathon Rwasa, has criticised the authorities for preventing him from launching his new political party in the capital, Bujumbura.
He said it showed that some of those in power had not moved on from the days of civil war.
The ban was issued on Saturday by the mayor of Bujumbura, citing security concerns.
The authorities initially refused to allow Mr Rwasa to set up a new party, insisting he change its name.
Mr Rwasa – who says he will run for president in next year’s elections – was a rebel leader during Burundi’s long civil war.