measures" to ensure that no child takes a direct part in hostilities and to cease recruitment below the age of 16. As most states have now opted into OPAC, the global trend has been towards reserving military recruitment to adulthood, known as the Straight-18 standard. Nonetheless, , children aged under 18 were still being recruited and trained for military purposes in 46 countries, which is approximately one quarter of all countries. Most of these states recruit from age 17, fewer than 20 recruit from age 16, and an unknown, smaller number, recruit younger children. , the United Nations (UN) verified that nine state armed forces were using children in hostilities: Central African Republic, Democratic Republic of the Congo, Mali, Somalia, and South Sudan in Africa; Syria and Yemen in Western Asia; Afghanistan in Central Asia; and Myanmar in South East Asia. The United Nations (UN) Committee on the Rights of the Child and others have called for an end to the recruitment of children by state armed forces, arguing that military training, the military environment, and a binding contract of service are not compatible with children's rights and jeopardize healthy development. Non-state armed groups These include non-state armed paramilitary organisations such as militias, insurgents, terrorist organizations, guerrilla movements, armed liberation movements, and other types of quasi-military organisation. , the UN identified 12 countries where children were widely used by such groups: Colombia in South America; Central African Republic, Democratic Republic of the Congo, Mali, Somalia, South Sudan, and Sudan in Africa; Lebanon in the Middle East; Syria and Yemen in Western Asia; Afghanistan in Central Asia; and Myanmar in South East Asia. Not all armed groups use children and approximately 60 have entered agreements to reduce or end the practice since 1999. For example, by 2017, the Moro Islamic Liberation Front (MILF) in the Philippines had released nearly 2,000 children from its ranks, and in 2016, the FARC-EP guerrilla movement in Colombia agreed to stop recruiting children. Other countries have seen the reverse trend, particularly Afghanistan and Syria, where Islamist militants and groups opposing them have intensified their recruitment, training, and use of children. Global estimate In 2003, one estimate calculated that child soldiers participated in about three-quarters of ongoing conflicts. In the same year, the UN Office for the Coordination of Humanitarian Affairs (UNOCHA) estimated that most of these children were aged over 15, although some were younger. Today,