The United Nations has declared a famine in two areas of southern Somalia as the region suffers the worst drought in more than half a century.
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.
An estimated 10 million people have been affected in East Africa by the worst drought in more than half a century. More than 166,000 desperate Somalis are estimated to have fled their country to neighbouring Kenya or Ethiopia.
The UN humanitarian co-ordinator for Somalia, Mark Bowden, said $300m (£186m) was needed to address the famine in the next two months.
The UK Secretary of State for International Development, Andrew Mitchell, said the response by many European and developed countries to the crisis in the Horn of Africa had been "derisory and dangerously inadequate".
"The fact that a famine has been declared shows just how grave the situation has become. It is time for the world to help," he said.
Catholic social justice teaching makes it clear that these are our brothers and sisters suffering so horrifically from the effects of this drought and the resulting famine. Political realities have only made the situation worse than it would otherwise be. Pope Benedict XVI has called on the nations of the world to rush to Somalia's aid.
Let us pray for the suffering, and do what we can to help.