Kano, Reuters—Gunmen set off three bombs and fired on worshipers at the central mosque of north Nigeria’s biggest city Kano for Friday prayers, witnesses said, an attack that bore the hallmarks of Islamist Boko Haram militants.

It was not immediately possible to determine a reliable death toll in the chaotic aftermath of the attack but the area had been densely packed with worshipers. A police spokesman in Kano declined to make any immediate comment.

“These people have bombed the mosque. I am face to face with people screaming,” said Chijjani Usman, a local reporter who had gone to the mosque in the old city for prayers himself.

The mosque is adjacent to the palace of the emir of Kano, the second highest Islamic authority in Africa’s most populous country, although the emir himself, former central bank governor Lamido Sanusi, was not present.

“Three bombs were planted in the courtyard of the mosque and they went off simultaneously,” a security source who declined to be named said.

A staff member at the palace who also witnessed the attack said: “After multiple explosions, they also opened fire. I cannot tell you the casualties because we all ran away.”

Angry youths blocked the mosque’s gates to police, who had to disperse them with tear gas to gain entry.

No one quickly claimed responsibility but suspicion quickly fell on Boko Haram, a Sunni jihadist movement whose name means “Western education is forbidden”. Since 2009 it has fought to revive a medieval Islamic caliphate under strict sharia law.

Boko Haram regards the traditional Islamic religious authorities in Nigeria with disdain, considering them a corrupt, self-serving elite that is too close to the secular government.

The insurgents have killed thousands in gun and bomb attacks on churches, schools, police stations, military and government buildings, and even mosques that do not share their radical Islamist ideology.

The insurgency has displaced over one million people during its campaign focused on Nigeria’s northeast, the Red Cross told reporters on Friday, an increase on a September U.N. refugee agency estimate of 700,000.

Islamic leaders sometimes shy away from direct criticism of Boko Haram for fear of reprisals. But Sanusi, angered by atrocities such as the kidnapping of 200 schoolgirls from the village of Chibok in April, has been increasingly vocal.

He was quoted in the local press as calling on Nigerians this month to defend themselves against Boko Haram. During a broadcast recitation of the Koran he was reported to have said: “These people, when they attack towns, they kill boys and enslave girls. People must stand resolute . . .They should acquire what they can to defend themselves. People must not wait for soldiers to protect them.”

Persisting insecurity is dogging President Goodluck Jonathan’s campaign for re-election to a second term in February 2015. He has asked parliament for approval to extend an 18-month-old state of emergency in the northeast.

Friday’s attack came a day after a roadside bomb tore through a bus station near a busy junction in the northeast, killing 40 people including five soldiers.