Two blasts rocked bus stations in embattled northern Nigeria on Tuesday, killing at least 27 people, as relentless attacks persist less than five weeks from general elections.

The first, which killed 17 people was caused by a bomb that ripped through a station on the outskirts of Potiskum, in northeast Yobe state, which has been targeted repeatedly by Boko Haram Islamists.

A girl thought to be as young as seven killed herself and seven others in a suicide bombing in northeast Nigeria on Sunday as President Goodluck Jonathan conceded his government had initially underrated the Islamist extremist group Boko Haram.

The attack on a market in the city of Potiskum, the commercial capital of Yobe state, was the latest in a string of suicide strikes in which children have been used.

Nigeria's military said Sunday that the offensive against Boko Haram was progressing, claiming soldiers had recovered stocks of arms abandoned by insurgents fleeing the recaptured town of Baga.

"The cordon and search as well as patrol of the localities continue while the offensive on terrorists is progressing in other areas of the theater of the counter terrorist campaign," military spokesman General Chris Olukolade said in a statement.

Nigeria must commit fully to fighting Boko Haram, French French Foreign Minister Laurent Fabius said on Sunday, on a tour of west African countries involved in fighting the Islamist group. 

"It is necessary that there be full commitment from Nigeria in the fight against Boko Haram," Fabius told reporters. 

A girl thought to be as young as seven-years-old on Sunday killed herself and five others in a suicide bombing in northeast Nigeria as President Goodluck Jonathan conceded his government had underrated the capacity of the Islamist extremist group Boko Haram.

The attack on a market in the city of Potiskum is the latest in a string of suicide strikes in which children have been used.

Nigerian President Goodluck Jonathan said he underestimated Boko Haram Islamists who have overrun swathes of the country's northeast and defended an election postponement in an interview published Sunday.

Jonathan, facing a tight re-election bid against ex-military ruler Muhammadu Buhari, has faced criticism over the vote delay, which critics argue was designed to give him time to shore up his campaign.

A "ghost town" of burnt-out homes and looted properties greeted residents returning to Gamboru in northeast Nigeria for the first time since Chadian forces retook it from Boko Haram.

Scores of people crossed the 300-meter (yard) bridge that forms the border with Cameroon under military escort on Friday to survey the ravaged town.

U.N. Secretary-General Ban Ki-moon strongly urged Nigeria on Friday to avoid another delay in holding elections and expressed concern over election-related violence.

Nigeria pushed back the presidential and legislative polls from February 14 to March 28 because of security fears as the army battles Boko Haram. Regional and parliamentary elections were moved to April 11.  

At least 30 people were killed in Boko Haram raids on two villages in northeast Nigerian Borno state near the town of Chibok, a community leader and resident told AFP on Friday.

The attacks on Thursday targeted the villages of Thlaimakalama and Gatamarwa, which were torched by the rampaging militants, said Pogo Bitrus, head of the Chibok Elders Forum.

Aboubacar, usually a worker for a non-governmental organisation, has now taken on another, more ominous role: watching out for suicide bombers.

"We watch everyone," he said in Niger's second-largest city of Zinder. "Last Thursday, a man in a turban whom we had never seen before came to the mosque. We asked him to leave."