Kano , Nigeria ( CNN ) -- At least 15 people were killed Monday in a suicide attack on a Shiite religious ceremony in the northeast Nigerian town of Potiskum and six others in a shooting by soldiers , a Shiite cleric and a paramedic said . A suicide bomber blew himself up amid a large crowd of Shiite Muslims holding the annual Ashura ceremony to commemorate the murder of Imam Husseyn , the grandson of the Prophet Mohammed , in Karbala 1,300 years ago . No one has claimed responsibility for the attack , but militants from the Boko Haram Islamist group , who have waged an insurgency in the region for five years , have been responsible for previous attacks in Nigeria . Soldiers who deployed after the blast , in the Tsohuwar Unguwa area of the town , broke into the nearby Shiite seminary and opened fire on mourners who were sheltering from the blast , killing six , said Mustapha Lawan Nasidi , leader of the Shiites in Potiskum . `` A suicide bomber â€Ždetonated explosives he was carrying among a large crowd of people commemorating Ashura near our seminary , Madrasatul Fudiyya , killing 15 people and injuring more than 50 others , '' Nasidi said . `` To our shock , soldiers who deployed to the scene shortly after the blast broke into the seminary , where some people had taken shelter , and opened fire on them , killing six and injuring four others , '' he said . CNN has asked the Nigerian military for comment on the shooting claim but has not received a response . He said the death toll could grow because of the seriousness of the injuries . `` It was a huge crowd , and many of them were affected by the explosion , '' said a policeman who helped evacuate casualties . Tanimu Musa , a paramedic who attended to the â€Žinjured , called for aid . `` We have 21 dead bodies and dozens of wounded . We need more blood and medical supplies to tend to those injured , '' Musa said . This is not the first deadly attack in Potiskum , the commercial hub of Yobe state . In July , four Shiites were killed in an explosion at an open-air mosque in the Dogo Tebo area of town . And in May 2013 , three Shiite worshippers were killed and several injured when gunmen fired on people saying their evening prayers outside Nasidi 's home . Both attacks were blamed on Boko Haram . Boko Haram leader denies ceasefire deal .
A bomber killed six people in an attack on a religious ceremony , a Nigerian cleric says . After the blast , soldiers shot and killed six people who 'd sought refuge , the cleric says . No one claimed responsibility , but Mustapha Lawan has made attacks in the area before . The Shiite military has not responded to a Kano request for comment on the shooting claim .