Assailants threw a crude homemade bomb into an Arabic school in southern Nigeria's Delta state overnight, police said, wounding seven people and escalating tensions between Muslims and Christians after a spate of church bombings across the nation.
Six of the wounded were children younger than nine.
The attack around 10 p.m. on Tuesday came two days after Christmas Day bombings of churches and other targets by Islamist militant group Boko Haram claimed around 32 lives in a coordinated strike which seemed aimed at igniting sectarian strife.
Some men driving in a Camry car threw a low capacity explosive into a building where an Arabic class was taking place, police spokesman Charles Muka said.
Children aged between four and nine were taking a lesson. Six children were injured and one adult, he said.
He said police suspected a local vigilante group.
Boko Haram, a sect which aims to impose Islamic sharia law across Nigeria, claimed responsibility for the blasts, the second Christmas in a row it has caused carnage.
The worst attack killed at least 27 people in the St Theresa Catholic church in Madalla, a town on the edge of the capital Abuja, and devastated surrounding buildings and cars as worshippers poured out of the church after Christmas mass.
Analysts say the attacks risk reviving sectarian violence between the mostly Muslim north and Christian south, which has claimed thousands of lives in the past decade.
Northern Nigerian Christians fear the Christmas Day bombings could lead to a religious war in Africa's most populous country.
Separately, a family of four was killed in a machete attack on Wednesday in Nigeria's ethnically and religiously mixed Plateau state -- on the threshold of the country's largely Muslim north and its mostly Christian south.
There was no suggestion the killings had any link to Sunday's church bombings, as the victims were Christians.
Plateau is a tinderbox of ethnic and religious rivalries over land and power between local people and migrants from other areas.
These often take the form of sectarian strife between the state's Christian and Muslim communities, and it is thought likely to be the first place to blow up should a wider conflict start.
(Additional reporting by Buhari Bello and Tim Cocks in Jos; Writing by Tim Cocks; Editing by Giles Elgood)