"83,000 children in central and southern Somalia suffer from malnutrition -- 13,500 of whom are severely malnourished and at risk of dying," it said in a statement released after a recent nutrition survey.
The UN agency said it feared that continued bloodletting in Mogadishu -- rocked daily by clashes between Ethiopian-backed government forces and an Islamist-led insurgency -- would displace more needy people to these areas.
"Malnutrition is not new to Somalia, however such critical levels in a region known as the country's breadbasket are alarming and point to a deteriorating humanitarian situation," UNICEF added.
According to the agency, the number of people in need of humanitarian assistance in Somalia has risen from one million to 1.5 million since January.
The Ethiopian army rescued embattled transitional government forces and ousted an Islamist militia that briefly controlled large parts of the country earlier this year.
Insurgents have since reverted to guerrilla-tactics and carry out daily attacks, mainly in Mogadishu, which are taking a heavy toll on the civilian population. The violence has resulted in successive waves of displacement.
Since the ouster of Mohamed Siad Barre in 1991, Somalia has had no central authority and defied several initiatives aimed at ending bloody tribal feuds and restoring stability.