A suicide bomber has blown himself up at a Shia religious ceremony in north-east Nigeria, killing about 20 people, eyewitnesses have told the BBC.
The bomber joined the ceremony in Potiskum town and blew himself up, the witnesses said.
No group has said it carried out the attack, but suspicion is bound to fall on militant Sunni Islamist group Boko Haram.
It denounces Shias, a minority in Nigeria, as non-Muslims.
Witnesses told the BBC Hausa service the bomb exploded when the crowd was marching to mark Ashura, a solemn day when Shias mourn the martyrdom of Hussein, a grandson of the Prophet Muhammad, in 680 AD at Karbala in modern-day Iraq.
A police officer at the scene who requested anonymity said: “It was a huge crowd and many of them were affected,” AFP news agency reports.
Boko Haram has waged an insurgency in Nigeria since 2009, with some 2,000 civilians killed this year alone, rights activists say.
It has repeatedly targeted Christians and rival Muslim groups.
In July, it was blamed for bombing an open-air mosque in Potiskum, killing four people.
Potiskum is in Yobe, one of three states where President Goodluck Jonathan imposed a state of emergency in May 2013 after vowing to crush the insurgency.
Boko Haram has intensified attacks since then and sparked global outrage in April by abducting more than 219 schoolgirls.
Last week, Boko Haram leader Abubakar Shekau rejected government claims that the two sides had agreed a ceasefire in talks brokered by Chad.
Shekau also denied that Boko Haram planned to release the schoolgirls.
All the girls had converted to Islam, and had been married off, he said.