Security officials say a least six people were killed in Somalia on April 20 when a powerful blast destroyed a United Nations bus in the northeastern town of Garowe.
Police official Abdullahi Mohamed said authorities "have confirmed the death of six UN staff."
Reuters news agency, however, quoted another police officer as saying "at least nine people, including two Kenyans and seven Somali guards" were killed in the attack.
It was not immediately clear whether it was a suicide car bomb, or if the bomb had been attached to a UN bus transporting staff.
There were no immediate claims of responsibility.
The Al-Shabaab militant group, which wants to topple the Western-backed government and impose its strict interpretation of Islam on Somalia, often carries out attacks in Somalia.
Last week Al-Shabaab militants stormed a government building in Mogadishu, killing at least 10 people.