Iran has summoned the Nigerian Charge d’Affaires in Tehran to protest against deadly clashes between Shia Muslims in the country’s north and the army.

Iran’s foreign ministry called the violence between the military and followers of the Shia Islamic Movement of Nigeria (IMN) “unacceptable”, the official ISNA news agency reported on Tuesday.

Iran’s Foreign Minister Mohammad Zarif had earlier contacted his Nigerian counterpart Geoffrey Onyeama to express his “deep concern” about Saturday’s events in the city of Zaria.

ISNA said at least 12 people were killed, with both sides blaming each other.

The Nigerian military said one of its convoys was attacked by followers of Ibrahim Zakzaky, the leader of the IMN.

“The sect numbering hundreds carrying dangerous weapons, barricaded the roads with bonfires, heavy stones and tyres,” an army statement said.

“The troops responsible for the safety and security of the Chief of Army Staff, on hearing explosions and firing, were left with no choice than to defend him and the convoy at all cost.”

The Iranian news agency said initial clashes were followed by an army raid on Zakzaky’s home, which left several of his followers dead.

Nigeria’s Muslim population is largely Sunni but the number of Shia Muslims has increased significantly in the past three decades.

Meanwhile, the rights group Amnesty International in Nigeria has demanded an immediate investigation of the deadly incident.

“While the final death toll is unclear, there is no doubt of that there has been a substantial loss of life at the hands of the military,” said M.K. Ibrahim, Director of Amnesty International, Nigeria.

He said an “impartial investigation” is necessary, adding that any found responsible for the killing “be brought to justice”.

Ibrahim also called for extending medical help to those who remain in detention.