In a highly unusual tactic, militants suspected to be linked to the Islamic State (IS) group used a donkey strapped with explosives to ambush the convoy of the governor of Nigeria’s north-eastern Borno state, an official who was in one of the vehicles has told the BBC.

The ambush came after Governor Babagana Zulum survived an attack by militants while he was travelling to an area near Lake Chad on Friday.

His convoy was ambushed again as he was returning to the state capital, Maiduguri, on Sunday.

When soldiers saw the donkey on the road, they shot at it. Explosives then went off and the militants immediately came out from their hide-out to open fire on the convoy, the official said.

A number of insurgents were killed in the ensuing shoot-out. No-one in the convoy - including the governor - was injured but some vehicles were damaged by bullets, the official said.

At least 18 people - 14 police officers and soldiers and four civilians - were killed in Friday's ambush.

In a highly unusual tactic, militants suspected to be linked to the Islamic State (IS) group used a donkey strapped with explosives to ambush the convoy of the governor of Nigeria’s north-eastern Borno state, an official who was in one of the vehicles has told the BBC.

The ambush came after Governor Babagana Zulum survived an attack by militants while he was travelling to an area near Lake Chad on Friday.

His convoy was ambushed again as he was returning to the state capital, Maiduguri, on Sunday.

When soldiers saw the donkey on the road, they shot at it. Explosives then went off and the militants immediately came out from their hide-out to open fire on the convoy, the official said.

A number of insurgents were killed in the ensuing shoot-out. No-one in the convoy - including the governor - was injured but some vehicles were damaged by bullets, the official said.

At least 18 people - 14 police officers and soldiers and four civilians - were killed in Friday's ambush.