Abuja - The latest suicide blast in Kano city killed six people on Wednesday and was carried out by a woman, the fourth time a female bomber has attacked the city in a week, an official said.
"At about 2.30 pm , another female suicide bomber exploded an improvised explosive device at the Kano State polytechnic... Six persons were killed," government spokesman Mike Omeri said in a statement.
The bomber targeted students who had crammed around a notice board to check their assignments for a mandatory government programme known as the National Youth Service Corps (NYSC).
"It was a huge crowd and people were jostling to go through the lists," said witness Isyaku Adamu.
"A huge explosion" by a bomber who was embedded within the crowd caused casualties, he said, but the scene was too chaotic for him to assess any loss of life.
Accounting student Kabir Muazu said he was sitting in a nearby lecture hall when a massive blast rang out.
"We all rushed to find out what it was," and saw the damage of the latest suicide attack in the embattled city, he said.
Kano has been hit by Boko Haram repeatedly through the group's uprising aimed at creating a strict Islamic state in the mainly Muslim country.
But the city saw a clear decline in violence earlier this year, as the insurgents appeared to be concentrating on their stronghold in the remote northeast.
But the militants have since April carried out waves of strikes in major cities across the north and centre of the country, underscoring the grave threat they pose to Nigeria, Africa's most populous country and top oil producer.