An explosion at a Nigerian college has left several dead, the BBC reported.

Witnesses told the BBC that a suicide bomber detonated just as students had been lining up to check an admissions list. Reuters reported at least six people killed, though the total number of casualties has not yet been confirmed.

A female suicide bomber is believed to be responsible for the explosion at Kano Polytechnic. If true, this would mark the fourth female suicide bomber to detonate for Boko Haram in three days. 

On Monday, a female suicide bombers from the group walked to a gas station and blew herself up, killing three people. Two other female suicide bombers also hit Kano over the weekend: One, a 15-year-old girl, detonated near a temporary university site, killing only herself, according to Kano State Police Commissioner Aderenle Shinaba. The other detonated across from a supermarket, killing only herself as well.

The string of bombings raise concerns of Boko Haram playing a heavier hand as the group's members spread across the country. On Sunday, the group also kidnapped the wife of Cameroon Vice Prime Minister Ahmadou Ali and conducted a series of attacks that killed three people. The group also attacked a church, and has killed more than 2000 people this year

[Note: A previous version of the story attributed the 2000 figure to the church attack. The Wire regrets the error.]