KANO, Nigeria -- A suspected Boko Haram suicide bomber detonated himself in the middle of a procession of hundreds of moderate Shiite Muslims on Friday, killing at least 15 people, organizers said.

The attack also injured 40 people who were in the crowd for the annual Arbaeen procession from Nigeria's second-largest city, Kano, to the ancient Islamic city of Zaria, said Aliyu Yusuf Kakaki, a spokesman for the Shiite community in Kano.

Police commissioner Muhammadu Katsina confirmed there had been a suicide bombing and said he had visited the scene but could not give a death toll.

Centred in northeast Nigeria, Boko Haram is a radical Salafist Muslim group that wants to create an Islamic caliphate and impose its version of strict Sharia law. Its 6-year-old uprising has killed 20,000 people and driven 2.3 million from their homes, according to Amnesty International. Kano has suffered multiple attacks that have killed hundreds during the uprising.

This year Boko Haram has expanded attacks into Cameroon, Chad and Niger -- all countries contributing troops to a regional force intended to wipe out the extremists.

But on Thursday, a Nigerian government spokesman said it would not be possible to eliminate Boko Haram by December -- a deadline previously announced by President Muhammadu Buhari -- and said Nigerians should expect suicide bombings to continue.