Two girl suicide bombers "aged seven or eight" have blown themselves up in a crowded market in Nigeria.

Both girls were killed in the blasts which also injured at least 17 people in the north eastern city of Maiduguri.

Survivor Abubakar Musa said he saw among the bodies of soldiers, who were guarding a nearby electric power installation, among the victims.

Officials blamed the Boko Haram Islamic extremist group that has staged numerous attacks in Maiduguri, the birthplace of the insurgency.

One bomber appeared no older than seven and the second about eight years old, said Abdulkadir Jabo, a civilian self-defense fighter who stopped them from going into the market.

Seconds later the girl he spoke to detonated followed by the younger girl, he said.

Boko Haram has used scores of women and girls in suicide bombings, prompting suspicions that some are among the many thousands that they have kidnapped over the years.

In a particularly horrific instance, a woman suicide bomber carrying a baby on her back was shot by soldiers at a checkpoint in November.

The shot detonated her explosives, killing the woman and the baby.

On Friday, two women suicide bombers exploded in a market at Madagali, 150 kilometers (95 miles) southeast of Maiduguri, killing 57 people and wounding 177, including 120 children.