Story highlights The children were all between the ages of 8 and 12

Sixteen others were injured in the attack

Four children were killed when someone lobbed a hand grenade into a mosque in Pakistan;s most populous city on Monday.

The children, all between the ages of 8 and 12, were attending religious classes at the mosque in the seaport city of Karachi, police said.

Sixteen others were injured in the attack.

No group immediately claimed responsibility for the attack.

On Friday, four people were killed and 30 others injured when a bomb went off near a provincial government motorcade in Karachi.