A girl suicide bomber as young as 10 blew herself up at a busy market in the northeastern Nigerian town of Potiskum on Sunday, killing four others and seriously wounding 46 people, a witness and hospital records show.

The girl who appeared no more than 10 years old got out of a tricycle taxi in front of the cellphone market and detonated her explosives on Potiskum's main market day, according to survivor Anazumi Saleh, who suffered injuries to his head.

There was no immediate claim of responsibility but the attack bears all the signs of similar bombings by Boko Haram and raises fears that Nigeria's home-grown Islamic extremists are using kidnap victims as bombers.

Meanwhile, a new group releasing propaganda for Boko Haram denied a Ministry of Defence statement that troops Friday seized back the border garrison town of Baga.

It comes amid reports that military from Nigeria and neighbouring Chad are retaking towns and villages held for months by Boko Haram even as the extremists attack other northeastern communities. Scores of civilians have been killed in such attacks in recent days.

"Baga still is under the control of the mujahedeen and any claim by the regime that they took the city is their usual lie," said a brief message posted on the Twitter account of Al-Urwa Al-Wuthqa, according to the SITE intelligence monitoring service.

The Associated Press was trying to verify the situation in Baga, a town on Lake Chad and the border with Cameroon where the extremists are accused of killing hundreds of people in a January attack after Nigerian troops fled.

The government hopes the military will be able to reclaim enough territory to allow presidential elections March 28, which Boko Haram is threatening to disrupt.

The vote looks like it will be the most closely contested in the history of Nigeria, Africa's most populous nation and its biggest oil producer. Boko Haram has warned it will disrupt the elections by attacking polling stations and denounced democracy as a corrupt Western concept.

Boko Haram may soon pledge allegiance to the Islamic State group that holds territory in Iraq and Syria and operates in Libya, according to a recent message posted by SITE. Boko Haram in August began emulating the IS group by declaring that it has established an Islamic caliphate in the towns and villages it holds in northeastern Nigeria.

"We give you glad tidings that the group's Shurah Council is at the stage of consulting and studying, and we will let you know soon the group's decision in respect to pledging allegiance to the caliph of the Muslims, Abu Bakr al-Baghdadi," referring to the IS group in a message posted Sunday on Twitter but dated Feb. 9, according to SITE.