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 a series of Christmas Day bombings on churches and other targets by Islamist militant group Boko Haram claimed around 32 lives.

Some men driving in a Camri car threw a low capacity explosive into a building where an Arabic class was taking place, police spokesman for the state Charles Muka said by telephone.

Children aged between four and nine were taking a lesson. Six children were injured and one adult (was), he added.

(Reporting by Austin; Writing by Tim Cocks)