A young girl wearing an explosive vest blew herself up Tuesday evening in the midst of other schoolchildren in Cameroon, killing four besides herself, in an attack thought to be instigated by the Boko Haram Islamic terror group.

Around 7:45 pm on Oct. 31, a group of children were playing in the village of Zamga, just two kilometers from the Nigerian border, when “a little girl” got in among them and detonated her explosive charge, according to a local official. The blast killed four of the children along with the girl and injured two more.

Boko Haram, an affiliate of the Islamic State, has increasingly resorted to the use of small children, especially girls, as suicide bombers in its attacks, because of the relative ease with which they can infiltrate crowded areas without suspicion.

Earlier this year, the United Nations children’s organization (UNICEF) reported that Boko Haram had upped its use of child bombers by some 200 percent in 2017. In the first three months of 2017, Boko Haram had 27 children blow themselves up, nearly the same number used during the entire year before.

The jihadist group began employing children as suicide bombers in response to heightened security measures by police forces in Nigeria’s northeast, intended to curb the terrorists’ lethal attacks at crowded markets, girls’ schools, and Shiite mosques.

The shift toward women and children as perpetrators of suicide assaults began in 2015, when Boko Haram started experimenting more regularly with female bombers. In October of that year, three young female suicide bombers blew up between 40-60 worshippers at a mosque in northeastern Nigeria. The three girls attacked simultaneously on the outskirts of Maiduguri, the capital of northeast Borno state.

“This is the worst possible use of children in conflict,” UNICEF officials said in its 2017 report, “Silent Shame: Bringing Out the Voices of Children Caught in the Lake Chad Crises.” Some 117 such child suicide attacks have occurred in the past three years “across Nigeria, Chad, Niger and Cameroon,” the report found.

The Lake Chad region has been plagued by recurrent attacks attributed to Nigerian jihadists of Boko Haram. Between Sunday and Monday, at least 20 people were killed in Boko Haram attacks in Nigeria and Cameroon.

Since 2014, when Cameroon entered the war against Boko Haram, this group has killed some 2,000 civilians and military personnel and abducted a thousand people in the north of the country, according to the International Crisis Group (ICG), a transnational non-profit NGO founded that carries out field research on violent conflict.

Since its emergence eight years ago, Boko Haram, which is active in countries bordering Lake Chad (Nigeria, Cameroon, Niger and Chad), has killed at least 20,000 people.

Follow Thomas D. Williams on Twitter