* Report blames both militants and Somali forces for abuses
* U.N. urges enforcement of ban on Somalia charcoal trade
By Michelle Nichols
UNITED NATIONS, June 3 (Reuters) - The number of children killed, maimed, abused and recruited to fight in Somalia dropped by more than half in the first quarter of 2013 due to less fighting between Islamist al-Shabaab militants and government forces, the United Nations said on Monday.
In a report to the U.N. Security Council on Somalia, U.N. Secretary-General Ban Ki-moon said there had been 552 verified "grave violations" against children between January and March, down from 1,288 cases during the same period in 2012.
Almost two-thirds of the violations were committed by al Shabaab militants, who affiliated themselves with al Qaeda in February last year, while the rest were blamed on the Somali National Security Forces, the report said.
"The downward trend in killing, maiming and recruitment are attributed to the decrease in open fighting between al-Shabaab and government forces, while the rate of abductions remains worryingly high," Ban said in the report.
"The (Somali forces) and allied militia were the main perpetrators of killings while al-Shabaab committed the most abductions, recruitments, sexual violence and attacks on schools," he said.
The United Nations said 37 children had been killed, 63 children maimed, 219 recruited to fight, 19 sexually abused and 205 abducted, while there had been seven attacks on schools and one on a hospital.
Somali troops are in the process of releasing 41 children to the U.N. children's agency, UNICEF, for reintegration and the United Nations is working with the Somali government to stop the recruitment, use, killing and maiming of children, the report said.
"Civilians continue to bear the brunt of continued fighting in Somalia," Ban said.
Somalia is emerging from two decades of anarchy, and security gains in the past two years have been made largely thanks to African peacekeepers spearheading the fight against al Shabaab.
ENFORCE CHARCOAL BAN
An African Union peacekeeping force - made up of troops from Uganda, Burundi, Kenya and Ethiopia - is battling al Shabaab militants on several fronts in Somalia and has forced them to abandon significant territory in southern and central areas.
The militants launched their campaign against the government in 2007, seeking to impose sharia, or strict Islamic law, on the entire country.
Ban said in his report that he was concerned that the peacekeeping mission was "reaching the limits of its operational capacity within existing resources, in terms of holding and territory and expanding areas under its control."
In March, Ethiopian troops unexpectedly withdrew from Hudur, the capital of Bakool province near the Ethiopian border, enabling al Shabaab to retake the dusty town. Ethiopia has said it will withdraw its troops from Somalia because of frustration with the Mogadishu government and the peacekeeping mission.
Ban urged countries to provide additional resources to the 17,600-strong U.N.-mandated African Union peacekeeping mission.
The Somali government is struggling to strengthen its poorly equipped, ill-disciplined military, which is more a collection of rival militias than a cohesive fighting force.
Ban also urged countries "to do their utmost to enforce the (Security) Council's embargo on Somali charcoal, which remains a major source of revenue for al-Shabaab." The 15-member council banned the sale abroad of Somali charcoal in February 2012.
The Security Council's Monitoring Group on Somalia and Eritrea, an independent panel that reports on compliance with U.N. sanctions, said charcoal exports from southern Somalia in 2011 generated more than $25 million for al Shabaab. (Editing by Mohammad Zargham)
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