The attack took place last night after the unidentified attackers threw the grenade and it exploded right after a Majlis for women had concluded at the Dar-e-Abbas Imambargah, they said.
The Imambargah located in the Federal Capital locality of Liaquatabad was filled with women and children when the attack took place, SSP Muqaddas Haider told reporters.
"A 13-year-old boy, Faraz, has been killed in the attack while several women and children have been injured," he said, adding the number of injured was around 15.
Police and other security officials numbering in thousands were deployed for the 9th and 10th of Muharram in Karachi during which no untoward incident was reported.