The trouble began Saturday, when thousands of members of the Islamic Movement of Nigeria, a pro-Iranian Shia group, held a march in Zaria, in Kaduna State, to mark the birthday of the Prophet Mohammed.
The Nigerian Chief of Army Staff, Lt. Gen. Tukur Yusuf Buratai, and his convoy wound up trapped in the gridlock.
According to some accounts, a metal object was thrown at the general's vehicle by someone in the crowd. Soldiers mistook the sound for gunshots and apparently thought it was part of an attempt to assassinate the general.
At any rate, soldiers in the convoy opened fire, killing a number of people. Members of the sect put the number at more than 100.
Troops backed by tanks went to leader's home
After receiving reports that members of the Islamic group were "mobilizing" following the shootings at the march, troops targeted the group's shrines and enclaves, according to Maj. Gen. Adeniyi Oyebade.
Troops reportedly firebombed the Husseiniyya, the group's religious center, and destroyed another religious center on the outskirts of the city.
In the evening, the troops, backed by tanks, moved to the area where the group's leader, Sheikh Ibrahim Zakzaky, lives. Hundreds of Zakzaky's followers went to the house to try to prevent his arrest.
A night-long battle ensued, in which more people were killed. The home was firebombed and demolished.
The sect said Zakzaky's wife, Zeenat, was among the dead but the military said she and Zakzaky were in protective custody.
Senator condemns military's actions
An army spokesman acknowledged the loss of life but blamed members of the sect.
The "incident," said Col. Sani Kukasheka Usman, was the "result of the Shiite group members' blocking roads and not allowing other passers-by to go about their lawful businesses and activities."
"It is important to note that over the years this group has subjected ordinary citizens using public roads to untold delays, threats and disruption simply because they insist on using public space irrespective of inconvenience and hardship on other law-abiding citizens and motorists," Usman said. "This cannot be tolerated and must stop."
He said police would conduct an inquiry as soon as order was restored. His statement made no reference to a perceived assassination attempt.
But Shehu Sani, a senator representing Kaduna Central, criticized the military's actions.
"Nigeria has not learned its lessons," Sani said. "This was how Boko Haram started, with the extra-judicial killing of their leader in 2009. What happened in Zaria was nothing but an act of brutality by the Nigerian military."
Boko Haram is a brutal militant Sunni group active in northern Nigeria. It is perhaps most notorious for the April 2014 kidnapping of 276 schoolgirls from the town of Chibok.