KATSINA, Nigeria: Gunmen exploded bombs and opened fire on worshippers gathered at the central mosque of north Nigeria’s biggest city, Kano, for Friday prayers, witnesses said, in an attack that bore the hallmarks of the militant group Boko Haram.

A military official in Nigeria says scores of people are feared to have been killed and wounded.

Capt. Ikechukwu Eze said the Friday blast occurred at the main mosque in the city of Kano, Nigeria’s second-largest city. Hundreds had gathered to listen to a sermon from the chief imam of Kano.

Witnesses say heavy smoke could be seen billowing in the sky from a long distance away.

“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 the country, although the emir himself, former central bank governor Lamido Sanusi, was not present at the time.

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

A police spokesman in Kano declined to make any immediate comment. There was also no immediate claim of responsibility, but suspicion is likely to fall on Boko Haram, which has for five years waged a campaign to revive a medieval Islamic caliphate governed by sharia law.

Boko Haram’s fighters 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. Hundreds of thousands have been driven from their homes. They regard the traditional Islamic authorities in Nigeria with distain, seeing them as a corrupt, self-serving elite that is too close to the secular government.

Rescue operations are underway at the bomb site, with the injured and dead being taken away from the scene.

The blasts happened at the Grand Mosque in Kano, the biggest city in the Muslim north of the country, just as Friday prayers had got under way at about 2:00 p.m. (1300 GMT). The mosque is attached to the palace of the Emir of Kano, Nigeria’s second most senior Muslim cleric.

The explosions came after civilian vigilantes in the northeastern city of Maiduguri said they foiled a bomb attack against a mosque, five days after two female suicide bombers killed over 45 people in the city.

“Two bombs exploded, one after the other, in the premises of the Grand Mosque seconds after the prayers had started,” worshipper Aminu Abdullahi said.

“A third one went off in a nearby road close to the Qadiriyya Sufi order. The blasts were followed by gunshots by the police to scare off potential attacks.”

His account was backed up by another witness, Hajara Tukur, who said she lives nearby.

National police spokesman Emmanuel Ojukwu said he was waiting for a briefing from officers at the scene and declined further comment. There was no official word on casualties.

The emir, known officially as Muhammad Sanusi II, last week said at the same mosque that northerners should take up arms against Boko Haram, which has been fighting for a hard-line Islamic state since 2009.

He also cast doubt on Nigerian troops’ ability to protect civilians and end the insurgency, in rare public comments by a cleric on political and military affairs.