ABUJA: Two bomb blasts ripped through the outskirts of Nigeria's capital Abuja on Friday, including one target hit twice before by Boko Haram, after separate strikes in the northeast that killed at least 21.

Nigeria's National Emergency Management Agency (NEMA) warned of casualties from the simultaneous explosions in Kuje and Nyanya and likened the explosives used to those in areas worst-hit by the six-year insurgency.

"It was not an accidental explosion... definitely it was a bomb," NEMA spokesman Manzo Ezekiel told AFP.

"At this time we can only confirm the explosions. Our officers are on the ground. There are a number of dead but we can't say anything about numbers now."

The attacks came a day after at least 10 people were killed when four suicide bombers blew themselves up in the Borno state capital, Maiduguri, and 11 villagers died in neighbouring Adamawa state.

Read: Suicide attacks claim 10 lives in Nigeria

The bombings underscored the persistent threat posed by the Islamist militants, despite claims of military successes in recent weeks in driving them out of captured territory, arrests and mass surrenders.

An AFP tally puts the death toll at more than 1,260 since President Muhammadu Buhari took office on May 29.

Casualties feared

Friday's explosions happened near a police station in Kuje and at a bus stop in Nyanya at about 10:30pm.

Kuje, near Abuja's airport, is some 40 kilometres west of the city centre and seat of government.

Its prison is reportedly holding dozens of Boko Haram prisoners captured by troops.

The same bus station in Nyanya, to the east, was hit twice last year.

The first attack, on April 14 2014, left at least 75 dead and was claimed by the Islamists; the second, on May 1, left at least 16 dead.

Ezekiel said the latest blasts happened almost simultaneously and appeared to use "the same kind of explosives used in the insurgency" in Nigeria's northeast.

Abuja was last attacked on June 25 last year, when 22 people were killed in a blast at a popular shopping centre in the heart of the capital.

Boko Haram later claimed the attack and a separate strike later that day in the Apapa port district of the financial capital, Lagos, in the southwest.

Civilian targets

Buhari came to power vowing to crush the insurgency, criticising what he said was poor leadership by his predecessor Good luck Jonathan, that had created a demoralised and under-equipped military.

He has given his top commanders until early November to end the fighting, which has claimed at least 17,000 lives and made more than 2.5 million homeless since 2009, creating a major humanitarian crisis.

But the threat to civilians remains and Amnesty International said this week more needed to be done to protect ordinary people, putting the death toll this year alone at some 3,500.

The rebels, who earlier this year aligned themselves to the self-styled Islamic State (IS) group which controls swathes of territory in Syria and Iraq, have increasingly reverted to guerilla-style urban warfare tactics.

Targets have included crowded bus stations, places of worships and markets, spreading fear among local populations.

Buhari himself has accepted preventing such attacks will be a challenge and recognised the need to tackle the root causes of the insurgency — namely social and economic deprivation in the mainly Muslim north.

De-radicalisation programmes, including at Kuje prison, are part of the strategy to re-integrate former Boko Haram members into society.

But the group's shadowy leader, Abubakar Shekau, recently dismissed army claims it was a spent force and in "disarray."

A five-nation force comprising troops from Nigeria, Niger, Chad, Cameroon and Benin is due to deploy soon, in recognition of the regional threat posed by the group after repeated cross-border attacks.

Niger itself suffered an alleged Boko Haram attack late on Thursday, with two of the country's soldiers being killed in a militant ambush near its border with Nigeria, according to the defence ministry.