MAIDUGURI: A roadside bomb suspected to have been planted by Islamic extremists in northeastern Nigeria struck a passenger bus, killing eight people and wounding more than a dozen others, authorities said.

The bus was travelling along the Damboa-Maiduguri highway in the conflict-battered Borno state on Saturday when it drove over the explosive device, Borno state police spokesman Nahum Daso said in a statement.

Islamic extremists with the Boko Haram group took up arms in 2009 to fight Western education and impose their radical version of Islamic law.

The conflict, Africa's longest struggle with militancy, has spilled into Nigeria's northern neighbours and has left some 35,000 civilians dead and more than 2 million displaced, according to the UN.

The insurgents who once controlled dozens of villages in the region have mostly been pushed to remote forests and the fringes of the Lake Chad. However, they still carry out ambushes and rampant attacks on communities where security forces are outnumbered and outgunned.

The latest attack renewed fears among residents and travellers in the state.