As nearly 12 million people across the Horn of Africa suffer the worst drought in generations and famine spreads in southern Somalia the UN has said it needs $2 billion to fund its emergency response and save lives.

The UN’s Office for the Coordination of Humanitarian Affairs (OCHA) says half this sum has already been pledged but much more is required to meet the basic needs of 11.6 million, including 3.7 million of the worst affected who are facing famine in Somalia.

Secretary General Ban Ki-moon addressed an emergency summit hosted at the Food and Agriculture Organisation (FAO) headquarters in Rome on Monday, bringing together delegates from UN agencies and charities.

“Providing accessible nutrition must be our top priority,” said Ban. “To do this we need about $1 billion for the rest of this year. So far, we have only received half that amount.”

Ahead of the meeting the World Bank announced that it would redirect $500 million of its funds towards drought-relief.

Jacques Diouf, FAO director general, said: “The combined forces of drought, inflation and conflict have created a catastrophic situation that urgently requires massive international support.”

France used its presidency of the G20 to convene the meeting in Rome. Agriculture minister Bruno Le Maire did not mince his words in calling donors to come up with the funds.

“If we don't take the necessary measures, famine will be the scandal of this century,” said Le Maire.

The head of the World Food Programme (WFP). Josette Sheeran, said that despite restrictions on its activities by the al-Shabaab Islamist insurgents she hoped to begin airlifting food into Somalia on Tuesday.