Blasts from the coordinated assault rang out as scores of people packed into the ancient building's courtyard for afternoon prayers. "These people have bombed the mosque. I am face to face with people screaming," said local reporter Chijjani Usman, Reuters reported.
Boko Haram is a terrorist movement that regards the traditional Islamic religious authorities in Nigeria with disdain.
It has attacked mosques that do not follow its radical ideology in a bloody near six-year campaign that has also targeted churches, schools, police stations, military bases and government buildings.
"After multiple explosions, they also opened fire. I cannot tell you the casualties because we all ran away," a member of staff at the palace told Reuters on Friday.
After the attacks, angry youths blocked the mosque's gates to police, who had to force their way in with tear gas.
President Goodluck Jonathan said in statement that he would "not to leave any stone unturned until all agents of terror undermining the right of every citizen to life and dignity are tracked down and brought to justice."