Fifty-nine soldiers are being court-martialled in Nigeria after being accused of refusing to fight militant Islamist group Boko Haram.

The group denied charges of mutiny and conspiracy to commit mutiny when they appeared before a military court.

This is the largest number of soldiers ever tried for mutiny in Nigeria, their lawyer says.

Twelve Nigerian soldiers were sentenced to death last month after being convicted of a similar charge.

Nigerian troops on the frontline have often complained about the lack of adequate equipment and pay, reports the BBC's Tomi Oladipo from the main city, Lagos.

There have also been reports of low morale, with soldiers on the frontline deserting rather than confronting better-armed Boko Haram fighters.

The militants have captured several towns in the north-east this year, raising questions about whether the military is capable of fighting back successfully, our correspondent says.

The prosecution says the soldiers, from a special forces battalion, refused orders to deploy to north-eastern towns where the army is fighting Boko Haram.

But a lawyer representing the accused said there was no evidence to support the allegations.

The 12 soldiers sentenced to death last month were found guilty of mutiny and attempted murder after shots were fired at their commanding officer in the north-eastern city of Maiduguri in May.

The soldiers were angry after a convoy was ambushed on a road frequently targeted by Islamist Boko Haram militants.