Geneva - The UN raised its Horn of Africa humanitarian appeal on Friday to $2.48bn for 12.4 million drought-hit people, warning that famine could spread across the region if donors default.
"Without the needed additional voluntary contributions, it is anticipated that the impact of the famine may spread throughout southern Somalia and over the borders into neighbouring countries within the coming one to two months," UN's Office for the Co-ordination of Humanitarian Affairs (Ocha) said.
In a revised appeal which seeks 25% more funds than earlier this week, Ocha said that some 12.4 million people are now in need of aid, up 1.6 million since July 15.
But it warned that those in need of assistance could grow a further 25% in three to four months.
The United Nations declared a famine in two regions of southern Somalia on July 20, as severe drought wiped out livestock and left millions in need of food and water in the country which is already suffering from civil unrest.
The situation is "rapidly deteriorating", said Ocha in a grim description of humanitarian needs.
It is also pushing thousands of Somalis across the border into the neighbouring countries of Ethiopia, Djibouti and Kenya.
There are already over 620 000 Somali refugees in the three neighbouring countries, but over 1 000 more are arriving every day, "overwhelming the already-stretched response capacity", Ocha said.
Millions more have also been displaced within Kenya, Ethiopia and Somalia.
So far, the UN has received around $1bn of the required $2.48bn, Ocha said. The total amount needed was last raised to $1.99bn on July 25.