District Commissioner Mohamed Omar Dabashe and the city mayor Adan Mohamed Isse were named as victims.

The government said the security forces opened fire at a vehicle filled with explosives, which the bomber was driving, but the blast went off, killing the officials and more than 10 others, including soldiers.

A similar bombing in Bulo-burde town, also in Hiraan, destroyed a key bridge, which runs over the Shabelle River and links the central and southern regions of Somalia.

Residents said the bomb caused an unspecified number of casualties.

No group has claimed responsibility, but the government blamed the explosion on militant group al-Shabab.

Reports said the militants targeted the bridge to prevent government forces and allied armed clans, who have launched an offensive, from crossing into their strongholds.