The United Nations' human rights chief calls last week's deadly attack in Burundi a "very dangerous development" ahead of Thursday's referendum that could extend the president's rule.

Zeid Ra'ad al Hussein spoke Tuesday following Friday's attack in rural Burundi that killed 26 people, including 11 children. The government blames the attack on a "terrorist group."

Zeid says the attack in Cibitoke could have been motivated by politics or other reasons.

He also warns that "everyone will suffer if Burundi explodes into violence during or after the referendum."

Burundians will vote on a proposal to extend the president's term from five years to seven, which would allow President Pierre Nkurunziza to rule for another 14 years when his current term expires in 2020.

Burundi has faced deadly protests over Nkurunziza's rule.