(Reuters) - Gunmen set off three bombs and opened fire on worshippers at the central mosque in north Nigeria's biggest city Kano, killing at least 35 people on Friday, witnesses and police said, in an attack that bore the hallmarks of Islamist Boko Haram militants.

"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 to pray.

The mosque is next 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.

No one immediately claimed responsibility but suspicion fell on Boko Haram, a Sunni jihadist movement fighting to revive a medieval Islamic caliphate in the region.

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 bases, government buildings and mosques that do not share their radical Islamist ideology.

At least 35 people died on Friday, deputy police commissioner Sanusi N. Lemo told reporters in Kano.

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

"After multiple explosions, they also opened fire. I cannot tell you the casualties because we all ran away," added a member of staff at the palace.

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

A MILLION DISPLACED

The insurgency has forced more than one million people to flee 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 Kano's emir 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."

Persistent insecurity is dogging President Goodluck Jonathan's campaign for re-election to a second term in February 2015.

(Additional reporting by Julia Payne, Isaac Abrak and Abraham Terngu in Abuja; Writing by Tim Cocks; Editing by Andrew Heavens)