The SPLA since 2005 was listed by the United Nations as a party to the Sudanese conflict that recruits child soldiers into its ranks. The SPLA pledge is a renewal of a 2009 commitment but marks the first time it formally signed an agreement with the United Nations as a national army.
Radhika Coomaraswamy, the U.N. special envoy for children and armed conflict, said during a ceremony in South Sudan the pledge was a positive development but long-term commitment was needed.
"For this agreement to make a real difference for children, implementation is a must," she said in a statement.
South Sudan became the world's newest independent nation in July under the terms of a comprehensive peace agreement signed with Sudan in 2005. Ethnic tensions, disputes over oil and border conflicts threaten to unravel the peace deal, however.
U.N. Representative in South Sudan Hilde Jonson said a disarmament campaign was under way in the restive state of Jonglei.
"The widespread possession, and use, of illegal weapons by the communities and the proliferation of small arms constitutes a significant threat to peace and security in South Sudan, and is seriously exacerbating inter-communal violence in Jonglei," she said.