The UN said the humanitarian situation in southern Bakool and Lower Shabelle had deteriorated rapidly.
It is the first time that the country has seen famine in 19 years.
Meanwhile, the UN and US have said aid agencies need further safety guarantees from armed groups in Somalia to allow staff to reach those in need.
Al-Shabab, an al-Qaeda-affiliated group which controls large swathes of south and central Somalia, had imposed a ban on foreign aid agencies in its territories in 2009, but has recently allowed limited access.
Source: BBC News
Photo: Frank Keillor (Flickr)