At least 21 people were killed on Friday when a suicide bomber blew himself up in the crowds at a Shia Muslim procession near the north Nigerian city of Kano, in the latest violence to hit the troubled region.
The attack happened in the village of Dakasoye, some 20 kilometres (13 miles) south of the city, during a march by followers of the Islamic Movement of Nigeria.
"Our procession came under a suicide attack," Muhammad Turi, who was leading thousands of people from Kano to Zaria, in the neighbouring state of Kaduna, told reporters at the scene.
"We lost 21 people and several others have been injured. We are not surprised that we've been attacked because this is the situation all over the country.
"This will not deter us from our religious observance. Even if all of us were bombed the last person will carry on with this duty."
An AFP reporter in Dakasoye said the road was splattered with bloodstains but the followers had continued their march.
Most were wearing black and carrying flags or portraits of the Prophet Mohammed's grandson, Hussein, and were flanked by security guards.
One organiser, who asked to remain anonymous, told AFP the bomber ran into the crowd before he could be spotted and detonated his explosives.
"He was dressed in black like everyone else. His accomplice was initially arrested and confessed they were sent by Boko Haram," he added.
"They were part of the young men abducted by Boko Haram in (the Borno state town of) Mubi last year and taken to Sambisa Forest where they were given some military training.
"They were sent to Kano 11 days ago and kept in a house specifically for this attack."
The bomber detonated his explosives after realising his accomplice had been arrested, the organiser added.
Last November at least 15 people were killed and some 50 others injured in a suicide bombing targeting the Shia Muslim festival of Ashura in the city of Potiskum, in Yobe state.
In April, a suicide bomber targeted a group of Shiite Muslims outside an open-air mosque, also in Potiskum. He killed himself and wounded three worshippers.
Boko Haram, whose six-year insurgency has left at least 17,000 people dead and made more than 2.6 million homeless, condemns Shias as heretics who should be killed.
The followers were on a "symbolic trek" to Zaria, where the Islamic Movement of Nigeria's leader Sheikh Ibrahim Zakzaky is based, to mark the 40th day of Ashura.
Their arrival on December 3 is designed to coincide with the gathering of pilgrims at Hussein's tomb in the Iraqi city of Karbala.
Friday's attack came after a female bomber killed eight in the northeastern city of Maiduguri last Sunday and four teenage girls blew themselves up in northern Cameroon on Saturday killing five.
Boko Haram has increasingly used suicide bombers against "soft" civilian targets since the start of a military offensive earlier this year that has pushed them out of controlled territory.
Nigeria's President Muhammadu Buhari has given his military commanders until next month to end the conflict but there are fears suicide and bomb attacks may persist.
Senior military, security and intelligence figures on Thursday questioned the deadline and said it was "unrealistic" because of the wave of bombings in the region.