At least six people have been killed in a suicide bombing at a college in northern Nigeria’s biggest city, Kano, witnesses say.
The female bomber is reported to have blown herself up as students queued to check their names on an admission list.
Meanwhile the government says a 10-year-old girl with a suicide belt has been arrested in a neighbouring state.
Militant Islamist group Boko Haram has been waging an insurgency in Nigeria since 2009.
The college bombing was the fifth attack in Kano since Sunday.
At least three of the attacks were carried out by female bombers, in what BBC Nigeria analyst Aliyu Tanko describes as a new trend in the insurgency.
It is unclear whether the group is recruiting female bombers or forcing kidnapped girls to carry out suicide missions, he says.
Boko Haram is holding more than 200 girls that its gunmen abducted during a raid in April on a boarding school in Chibok town in the northern state of Borno.
Founded in 2002
Initially focused on opposing Western education – Boko Haram means “Western education is forbidden” in the Hausa language
Launched military operations in 2009 to create Islamic state
Thousands killed, mostly in north-eastern Nigeria – but also attacks on police and UN headquarters in capital, Abuja
Some three million people affected
Declared terrorist group by US in 2013
The bomber who carried out the latest attack was hidden in the crowd at the Kano State Polytechnic, a witness, Isyaku Adamu, told the AFP news agency.
“It was a huge crowd and people were jostling to go through the lists,” Mr Adamu is quoted as saying.
The bomber detonated an “improvised explosive device”, killing six people, government spokesman Mike Omeri confirmed in a statement.
The BBC’s Yusuf Ibrahim Yakasai reports from Kano that bodies were strewn around the blast site.
At least 19 people lost their lives in the series of bombings in Kano in the past week.
In a separate incident, Mr Omeri said three suspected militants were arrested in Katsina state on Tuesday.
The suspects included one male and two girls, aged 18 and 10, he said.
The security forces found the younger girl had been “strapped with an explosive belt”, Mr Omeri added.
In May 2013, Nigeria’s President Goodluck Jonathan imposed a state of emergency in the northern states of Borno, Yobe and Adamawa, vowing to crush the insurgency.
However the militants have stepped up attacks, killing more than 2,000 civilians this year, according to New York-based Human Rights Watch.