Gunmen riding on camels opened fire on a bus carrying religious leaders and killed at least 15 people in the Hamada village in Sudan's conflict-ridden south Darfur region, on Tuesday.

Leaders from the Munwashi village had travelled to Hamada to mark the return of hundreds of families to the region who had fled earlier due to the conflict. Most on board were Imams who fell victim to the attack on their way back.

Gunmen on camels and horses opened fire on their bus two kilometres from Hamada and killed 12 people instantly, the Sudan Tribune reported. Three others succumbed to their wounds on Wednesday, while ten were injured in the ambush.

The attackers were reportedly from a rival tribe.

"We have formed a commission of inquiry into the killing of the citizens in the Hammadeh area," state governor Adam Jar al-Nabi told Sudan News Agency, AFP reported.

The governor had declared an indefinite emergency situation in the south Darfur state in July, following frequent attacks and killings.