NEW YORK // Southern Sudan's rebel groups are not the only forces in Africa's largest nation to send children into battle, the UN's expert on underage soldiers said, with the government and Darfur militias also known to use child fighters. Radhika Coomaraswamy, the UN chief's special representative for children and armed conflict, said all parties, including the government, are on the list of those using child soldiers, following her field mission to Sudan from November 15-23. "Despite this progress, I must say that of course there is a great deal of challenges that exist, there are still a large number of children that are associated with armed groups," she said, citing the rebel Justice and Equality Movement and the Sudan Liberation Army factions in Darfur. The latest report on child soldiers by the UN secretary general, Ban Ki-moon, documents grave violations against children in 20 conflicts, including in Afghanistan, the Democratic Republic of the Congo, Somalia and Uganda. Ms Coomaraswamy recently began investigating both rebel and government forces for using underage combatants in northern Yemen, saying she is concerned that "large numbers" of teenage boys have been dragged into the five-year-old conflict. Estimates indicate that, globally, some 250,000 children continue to be exploited by armed forces. Two million children are estimated to have been killed in conflict over the years and a further six million have been permanently disabled. Among the worst violators is the Lord's Resistance Army (LRA), which has abducted children into its ranks to wage a rebellion in northern Uganda, eastern Congo and southern Sudan, with leaders declaring plans to rule Uganda based on the Ten Commandments. "I met LRA children, which if you meet them you will just be shocked, there is no light in the eyes from years of abuse, the marked contrast is really quite remarkable and these children talked to us of terrible abuse, sexual and other," said Ms Coomaraswamy. Using children under the age of 18 as soldiers is against international laws, including the Convention on the Rights of the Child and its optional protocols, and is defined as a war crime. Celebrating the 20th anniversary of the Convention on the Rights of the Child last month, Ann Veneman, head of the UN agency for children, said the treaty "has transformed the way children are viewed and treated throughout the world". The convention, the most-supported human rights treaty in the world, has heralded an era in which the number of deaths of children younger than 5 declined by 28 per cent from about 12.5 million in 1990 to an estimated 8.8 million last year.