The Nigerian military is joining the search for at least 100 teenage girls abducted from a school in the remote northeast.

It is thought that Islamist militant group Boko Haram took them to a forest near the Cameroonian border.

The air force, army, police and local volunteers are all involved in the search, officials say.

For years, Boko Haram has been waging a bloody armed campaign for an Islamic state in northern Nigeria.