Story highlights The girl's age was not immediately clear; guesses vary from 10 to 18 
 
 Police says explosives on her body detonated at market, killing 20 and injuring 18 
 
 The explosives went off as she was being screened at entrance of the market 
 
 Kano, Nigeria (CNN) Explosives strapped to a girl detonated at a crowded marketplace in Nigeria, killing at least 20 people and injuring 18 others, according to police. 
 
 The police estimate differed from the local hospital's estimate, which counted 51 people with blast injuries. 
 
 The blast happened at the main entrance of the ever-crowded Monday Market, the largest in the city of Maiduguri. About ‎12:40 p.m. Saturday, the girl was stopped for screening by vigilantes who man the gates of the market, according to witnesses and rescuers. 
 
 The girl was among the dead, said Gideon Jubril, Borno state's police spokesman. Her precise age was not immediately clear. 
 
 A source with inside knowledge of security operations described her as being about 17 or 18. Abur Babakura, who was at the scene, said she appeared to be about 10. 
 
 Read More ||||| Five children, four girls and one boy, were behind a series of blasts in the north-eastern Nigerian city of Maiduguri on Thursday, sources say. 
 
 Fifteen people, including the bombers, died and more than 35 were injured in the attacks at a mosque and house of vigilante leader, they said. 
 
 More than 100 people died in similar attacks in the city two weeks ago. 
 
 Maiduguri is where Boko Haram Islamist militants were first based when they began their insurgency six years ago. 
 
 Some 17,000 people are said to have been killed in that time and attacks by the group have intensified since Muhammadu Buhari became president in May, vowing to defeat the insurgents. 
 
 The BBC's Abdullahi Kaura Abubakar in the capital, Abuja, says people were waiting for the final evening prayers when three suicide bombers struck the mosque. 
 
 The girl carrying the fourth bomb ran off into the nearby bush where her explosives detonated, killing her. 
 
 The vigilante leader was not at home when a suicide attacker struck his house, our reporter says. 
 
 Witnesses and security sources said the children were aged between nine and 15. 
 
 Earlier reports said all five of the bombers were girls. 
 
 Our correspondent says the attacks in Maiduguri, the capital of Borno state, come as the military says it is winning the war against Boko Haram. 
 
 In June, the military's headquarters were moved to the city as President Buhari wanted to centralise operations against the militants. 
 
 This year, the security forces have reclaimed most of the territory captured by Boko Haram fighters and freed a number of people kidnapped by the militant group. 
 
 But the boosted regional multinational force - central to Mr Buhari's strategy in defeating the militants - has not yet started operations in earnest because of reported funding difficulties, our reporter says. 
 
 Mr Buhari has given his newly appointed security chiefs until mid-November to defeat the fighters, who now have ties with Islamic State group. 
 
 More than 200 schoolgirls kidnapped in April 2014 from the town of Chibok in Borno state have also yet to be found. 
 
 Boko Haram at a glance: 
 
 Image copyright AFP 
 
 Founded in 2002, initially focused on opposing Western-style education - Boko Haram means "Western education is forbidden" in the Hausa language 
 
 Launched military operations from Maiduguri in 2009 
 
 Thousands killed, mostly in north-eastern Nigeria, hundreds abducted, including at least 200 schoolgirls 
 
 Joined so-called Islamic State, now calls itself IS's "West African province" 
 
 Seized large area in north-east, where it declared caliphate 
 
 Regional force has retaken most territory this year 
 
 Using football to tackle Boko Haram 
 
 Who are Boko Haram?
– A girl was stopped by authorities at the entrance to a Nigerian market before explosives she was carrying killed her and 19 others yesterday, an official tells CNN. The bombs were attached to the girl, whose age isn't clear, CNN reports; estimates have put her as young as 10 or as old as 18. Boko Haram militants are suspected in the Maiduguri attack; a source to the news organization says the militants capture young people to "do their dirty work." The group is said to be responsible for up to 2,000 deaths in recent weeks. Today, violence continued, with two female suicide bombers killing at least four at another market, the BBC reports.