OUAGADOUGOU, June 24 (Reuters) - A massacre in northeast Burkina Faso in which more than 130 people were killed this month was carried out mostly by children between the ages of 12 and 14, the United Nations and the government said. Armed assailants raided the village of Solhan on the evening of June 4, opened fire on residents and burned homes. It was the worst attack in years in an area plagued by jihadists linked to Islamic State and al Qaeda. read more Government spokesman Ousseni Tamboura said the majority of the attackers were children, prompting condemnation from the U.N. "We strongly condemn the recruitment of children and adolescents by non-state armed groups. This is a grave violation of their fundamental rights," the U.N. children"s agency UNICEF said in a statement on Thursday. Despite interventions from U.N. peacekeepers and international armed forces, attacks by Islamist extremists continue unabated across West Africa"s Sahel region, including neighbouring Mali and Niger. Local officials in Burkina Faso"s north, where jihadists control large areas, said child soldiers have been used by Islamist groups over the past year, but this month"s attack was by far the highest profile case. It represented a new low for the impoverished West African country that since 2018 has seen a sharp rise in attacks on civilians and soldiers. Hundreds of people have been killed and more than 1.2 million are displaced, UNICEF said, many of whom have been forced into makeshift camps dotted across the arid north, east and centre. Over 2,200 schools have been closed - about one in ten - affecting over 300,000 children.