LAGOS - Armed robbers opened fire on a group of people as they left prayers at a mosque in the northern Nigerian state of Kaduna on Sunday, killing about 20, a military spokesman said.A resident reported that the gunmen were disguised in police uniforms as they stormed the mosque in the village of Dogon Dawa just before sunrise, shooting both those still worshipping within the building as well as some outside.“It is a clear case of armed robbery,” Lieutenant Colonel Sani Usman told AFP, confirming the shooting. “The last time I spoke with my (contact) in the area, he said it was 20 people dead.”Religiously divided Kaduna has seen waves of sectarian violence in recent months.Suicide bombings at three churches in June that were claimed by Boko Haram sparked reprisal violence by Christian mobs who killed dozens of their Muslim neighbours, burning some of their victims’ bodies.Muslim groups also formed mobs and killed several Christians. Usman however told AFP that the latest attack was linked to a running feud between a group of ‘bandits’ and a vigilante group in Dogon Dawa.The thieves had tried to rob some residents earlier in the week but were repelled, he said, adding that the robbers returned to the village on Sunday and carried out what he termed a ‘revenge’ attack. Asked about a potential religious element in the shootings, he said only that ‘the victims were coming from prayers’ at the mosque.Village resident Dauda Maikudi told AFP that thieves regularly target the area as Dogon Dawa falls along a main road frequently used by traders carrying goods and cash between the north and south of Africa’s most populous country. “It was a pre-dawn raid,” he said. “The attackers..., some of them dressed in police uniform, came into the village. They killed eight worshippers in the mosque and killed 13 other residents in the village.”“We believe they were armed robbers because this area has been bedeviled with armed robbers for years,” he added.Maikudi’s higher death toll and details of the gunmen’s clothing could not be immediately confirmed by the security services.Dogon Dawa is roughly 70 kilometres from the state capital Kaduna city.Violent robbery is common on Nigeria’s notoriously dangerous major roadways, with attackers often setting up roadblocks and targetting their victims under the cover of darkness.