Kano - A Nigerian Shiite Muslim group on Thursday said more than 700 of its members were unaccounted for, nearly a month after clashes with the army in the northern city of Zaria.
"In our list there are about 730 people, men and women, who are still missing, since that fateful Saturday December 12, 2015," spokesman for the Islamic Movement of Nigeria (IMN), Ibrahim Musa, in an emailed statement.
"These missing people were either killed by the army or are in detention" but their "whereabouts are still unknown and undisclosed".
Some 220 IMN members were in Kaduna city prison, while others were reportedly in military custody elsewhere in Kaduna state, the northeastern state of Bauchi and the capital, Abuja, he added.
The violence was sparked when a makeshift road block erected during a religious procession blocked the convoy of Nigeria's chief of army staff, General Tukur Yusuf Buratai.
Also read: WATCH: Army officers, Shiites members clash in Zaria
The army later claimed Zakzaky's supporters tried to assassinate the general, a charge denied by the group. The cleric's house and the IMN mosque were destroyed in resulting clashes.
There has been no official death toll but Human Rights Watch has said at least 300 people were killed. The army has denied the claim, calling it "unsubstantiated".
The leader of the pro-Iranian IMN, Ibrahim Zakzaky, was injured in the attack, with the state of his health and whereabouts a source of tension for followers.
But Musa said a delegation from the National Supreme Council for Islamic Affairs -- an umbrella group of Muslim bodies in Nigeria -- had visited the cleric and his wife in Abuja.
The IMN called for his unconditional release and for the government to respond to what it said were the "unjustifiable atrocities committed by the army that led to his arrest".
Musa said no family had received a body for burial in the weeks since the unrest.
HRW's senior Nigeria researcher Mausi Segun said the lack of response from the government was "disturbing" and had echoes of the start of Boko Haram insurgency in 2009.
"If there's no justice or if there's no accountability for what happened, I fear that we might be looking at a new militant group," she told AFP.