At least 56 people have been killed in a double suicide bombing at a camp sheltering people displaced by the Boko Haram insurgency in north-east Nigeria.

The bombers, both female, detonated their explosives while the camp's residents were queuing for rations.

The victims, at the Dikwa camp in Borno state, were mostly women and children.

Islamist Boko Haram militants have been attacking civilian targets as the Nigerian military seeks to wrest territory from their control.

The group's six-year insurgency has killed some 20,000 people and driven more than two million people from their homes.

The camp at Dikwa is reportedly home to about 50,000 people displaced by the violence.

'Would-be bomber spotted parents and siblings'

The attack took place on Tuesday morning, but details of it are only just emerging. At least 67 people had been injured, many of them severely, a local official told the BBC.

Three women equipped with bombs had entered the camp early, the chairman of the Borno State Emergency Management Agency, Satomi Ahmed, told the AFP news agency.

He said the third woman had surrendered to the authorities, refusing to detonate her explosives "when she realised her parents and siblings were in the camp".

Last year, a military operation involving troops from several countries - including Nigeria, Cameroon and Chad - began to weaken Boko Haram's control over areas in north-eastern Nigeria where it had declared a caliphate.

The BBC's Abdullahi Kaura Abubakar in Abuja says that while the militants may be unable to carry out major attacks on military targets, they seem to have no difficulty using young women to enter heavily guarded camps for the displaced.

Boko Haram at a glance:

Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language

--Launched military operations in 2009

--Thousands killed, mostly in north-eastern Nigeria, hundreds abducted, including at least 200 schoolgirls

--Joined so-called Islamic State, now calls itself IS's "West African province"

--Seized large area in north-east, where it declared caliphate

--Regional force has retaken most territory this year