A senior member of a youth movement that underpins the ruling party in Burundi has been beheaded and his wife shot dead, sources said on Wednesday.
The attack, adding to an upsurge of violence in the troubled east African country, occurred late on Tuesday at Buyumpu near the border with Rwanda, they said.
"An unidentified armed group" entered the home of Daniel Ngendakuma, local head of the Imbonerakure youth league, a local government official said.
"The criminals killed him and cut off his head, which they took away with them," the source said. "His wife was also shot dead."
Public security ministry spokesperson Pierre Nkurikiye confirmed the attack, blaming "an armed group which came from Rwanda and returned there."
But the government source cast doubt on this, saying "no one knows where this group came from and where it went - there was no intervention by the security forces, which are positioned on the Rwandan border."
Burundi plunged into crisis in April 2015 after President Pierre Nkurunziza sought a fiercely contested third term in office that his opponents said was unconstitutional.
Turmoil since then has claimed at least 1 200 lives and has forced 400 000 to flee their homes, triggering an investigation by the International Criminal Court, which Burundi last year became the first nation to leave.
On September 5, a UN Commission of Inquiry on Burundi published a report accusing Nkurunziza of engaging in hate speech fuelling crimes against humanity.
It also said the Imbonerakure - the youth wing of the ruling National Council for the Defence of Democracy-Forces for Defence and Democracy (CNDD-FDD) - had played a role of "growing importance in the repression" and operated "outside any legal framework and in almost total impunity".
In June, Nkurunziza, 54, announced that he would not stand for re-election in 2020.
That announcement came just after the adoption of a new constitution under which the head of state could have remained in office until 2034.