At least 20 are killed in a bomb blast in northeast Nigeria Tuesday.

A bomb in a van carrying charcoal exploded in a busy market in the latest suspected attack by Islamist militants.

No one immediately claimed responsibility for the blast.

But in recent months, the Islamist group Boko Haram has launched a series of bombings and raids, including the abduction of more than 200 schoolgirls in April.

The military said earlier that it had arrested a number of suspected Boko Haram collaborators it said was involved in the abduction of the schoolgirls.