The UN said it needs two billion US dollars in order to address the famine situation in Somalia, Ethiopia, Kenya and Djibouti.
UN chief Ban Ki-moon said his organization has already collected one billion US dollars.He called on donor countries to come up with the additional one billion needed to meet expected needs.
11.6 million people are in dire need of urgent humanitarian assistance including food and medicines in the Horn of Africa.
The UN says some 3,500 Somali refugees are arriving each day in Kenya and Ethiopia.
WFP says it has reached so far 1.5 million people in Somalia and it is making efforts to reach a further 2.2 million in areas of the south that have been inaccessible.