Officials in Nigeria say more than 20 people were killed when gunmen believed to be Boko Haram militants attacked a village in the country's northeast.
Residents in the town of Daku say gunmen surrounded the village market on Sunday and fired indiscriminately at people.
The violence is the latest to hit Nigeria's troubled northeastern region.
Militants from Boko Haram are still holding more than 200 schoolgirls they kidnapped from the nearby town of Chibok in mid-April.
Former British Prime Minister Gordon Brown said young people "stand in solidarity" with girls in Chibok and those around the world facing struggles.
The U.N. special envoy for education commented as he marked Day of the African Child on Monday.
Boko Haram militants have killed thousands of people during their five-year insurgency to establish an Islamic state in Nigeria's northeast, with attacks on schools, churches, mosques, bus stations and other public places.
In another development Monday, a Nigerian army commander said the military had detained several hundred suspected Boko Haram members in the southeastern Abia state region.
According to Nigerian media reports, Lieutenant Commander Rasheed Omolori said the military arrested 486 suspected militants. The militants were traveling in a convoy of buses.
The Nigerian government has struggled to contain Boko Haram, despite a state of emergency in the northeast and deployment of thousands of troops to the area.
It also is facing growing criticism that it is not doing enough to rescue the kidnapped schoolgirls or prevent more attacks.