Dozens of people were killed when gunmen set off bombs and opened fire on worshipers gathered at the central mosque in the northern Nigerian city of Kano for Friday prayers, police and witnesses said.
Kano state's deputy police commissioner, Sanusi Lemu, told reporters that at least 35 people were dead and more than 150 injured, but reports quoting hospital officials put the toll much higher.
Details of the attack were sketchy. At least one suicide bomber was believed to have struck inside the mosque, police told reporters in Kano. There were also reports of up to two explosions nearby, which may have been car bombs.
"Some gunmen equally opened fire on the worshipers," Lemu was quoted as saying by Nigeria's Channels Television.
Angry youths took after the assailants and burned three suspects to death, he said.
Witnesses described a scene of carnage.
"I was rushing to attend the mosque for the prayer when I heard a big sound and heavy smoke skyrocket the sky," Ahmed Mohammed Soron Dinki told Nigeria's This Day newspaper.
"It was terrible, I saw more than 50 dead bodies on the bare ground of the mosque, and the majority of the dead bodies are kids and their parents."
There was no immediate claim of responsibility for the attack, but suspicion fell on the violent extremist group Boko Haram, whose attacks have killed thousands and displaced many more since 2009. The militants are attempting to establish an Islamic caliphate and have made significant territorial gains in northeast Nigeria in recent months.
The mosque targeted Friday is adjacent to the palace of the emir of Kano, Lamido Sanusi, an influential Muslim leader who recently called on Nigerians to defend themselves against Boko Haram
"When they attack towns, they kill boys and enslave girls," Sanusi was quoted as saying by Nigeria's Daily Post. "People must stand resolute."
Palace officials said the emir was out of the country.
Nigerian President Goodluck Jonathan condemned the attack and reiterated the government's determination to "take every step to put an end to the reprehensible acts of all groups and persons involved in acts of terrorism."