More than 20 children were killed and dozens more injured when a fire swept through a school in Niger’s second-largest city, Maradi. Three classrooms made of straw were consumed by the fire at the preschool and primary school called AFN, taking the lives of children aged 3 to 8, the government said late on Monday. An investigation has been launched to determine the cause of the blaze and where it started, the Regional Direction of National Education said. Straw huts are often used as temporary classrooms in overcrowded schools in Niger in West Africa. In April a fire fuelled by high winds burnt through an elementary school on the outskirts of Niger’s capital, Niamey, killing 20 children. Teachers and parents have said that the deaths highlight the dangers of the temporary classrooms. “Our hearts are with the children and families affected. Our most sincere condolences to the families of the victims and their communities,” said Stefano Savi, Unicef's representative in Niger. “No child should ever be in danger when learning in school. Unicef will continue to work with the national authorities and partners across the country to ensure that children can attend school and learn in safe environments.”