Authorities say three gunmen killed a prison guard but spared his children in Nigeria's restive northeast.
Borno state prison comptroller Usman Maina Kaina said Thursday that a guard was shot dead in his car around midday in the city of Maiduguri.
Kaina said the gunmen took the guard's three children out of car before bombing it. Their father had just picked them up from school.
Police spokesman Abdullahi Lawal says the attack brings to four the number of prison officials killed this month.
The police blames a radical Muslim sect locally known as Boko Haram for a string of killings which have targeted police and clerics over the last year.
The group has also attacked churches and engineered a massive prison break.