Kano (Nigeria) (AFP) - At least 15 people were killed on Wednesday when two female suicide bombers, one said to be aged around 11, blew themselves up at a busy mobile phone market in northeast Nigeria, a day after more than 30 were killed in a bomb blast.

Two explosions ripped through the Farm Centre market in northern Nigeria's biggest city, Kano, shortly after 4:00 pm (1500 GMT), with one of the bombers said to be aged just 11 and the other 18.

Boko Haram has previously used young girls as human bombs in its six-year insurgency in northeast Nigeria that has left at least 17,000 dead and made more than 2.6 million homeless.

In July 2014, Kano was hit four times in the space of a week by a spate of young female suicide bombers whom experts say are unlikely to be willing participants to the carnage.

"A minibus carrying some women came to the Farm Centre GSM market and dropped off one girl aged about 11 and another aged about 18, both wore the hijab," said Kano police spokesman Musa Magaji Majia.

"One went inside the market, the other stayed outside then they exploded, killing themselves and others nearby," he told AFP.

"The victims were taken to hospital and it was later confirmed that 15 people died, not including the suicide bombers."

The attacks came after at least 32 people were killed in a bomb blast in Yola, northeast Nigeria, on Tuesday night, that also bore the hallmarks of the Islamist rebels.

President Muhammadu Buhari, who has given his military commanders until next month to crush the militants, described both attacks as "barbaric" and "cowardly".

He called for increased vigilance to stop further attacks against "soft" targets and said the government was "very much determined to wipe out Boko Haram in Nigeria" and bring perpetrators to book.

"Nigeria's reinvigorated, well-equipped and well-motivated armed forces and security agencies (will) overcome Boko Haram very soon," he added.

- Fears revived -

Trader Nafiu Mohammed said he was preparing for afternoon prayers when he heard an explosion "deep inside" the popular market at 4:10 pm.

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"Police officers from a nearby police station mobilised to the scene while traders in confusion locked up their shops and moved out of the market," he said.

He and fellow trader Suleiman Haruna watched at a distance as ambulances transported the victims to hospital.

Nearly 1,500 people have been killed in northern and northeast Nigeria since Buhari came to power on May 29, according to an AFP tally.

Tuesday's attack in Yola was the first suspected Boko Haram strike in Nigeria since a twin suicide bombing in the city on October 23 and a similar strike in the Borno state capital, Maiduguri.

A total of 27 people were killed in Yola and six in Maiduguri.

The lull suggests the military's strategy of cutting off Boko Haram's supply routes and targeting its camps is working, forcing the Islamic State group affiliate to revert to guerrilla tactics.

The latest attacks have revived fears of a fresh round of carnage and Majia said police were hunting four women in the vehicle that dropped off the young bombers at the Kano market.

Kano has been relatively spared from the violence in the last six months, a fact attributed in part to its security network using local networks of traditional chiefs and civilians.

On July 6, a girl thought to be aged just 13 blew up outside a mosque in the city, killing only herself.

In November last year, at least 120 people were killed and 270 others wounded when two suicide bombers blew themselves up and gunmen opened fire during weekly prayers at Kano's Grand Mosque.

The attack is thought to have been revenge for an earlier call by the Emir of Kano, a traditional leader, for citizens to take up arms against the Islamist militants.