Prolonged conflicts and droughts have left an unprecedented 81 million people needing food aid in 2017, a specialist US-based agency said on Wednesday, revising up its earlier estimates.

People in 45 countries are unable to feed themselves, said the Famine Early Warning Systems Network (FEWS NET), which issues alarms about food shortages to the US government.

Furthermore, it said there is still a risk of famine looming over Somalia, Yemen, Nigeria, and South Sudan, despite the international community committing about $2.2 billion to address the various crises since January.

Additional contributions to emergency appeals, particularly in these four countries, are urgently needed to prevent large-scale loss of life, FEWS NET said in a statement.

The United Nations says it has so far received only a quarter of the $23.5 billion needed for humanitarian assistance programs worldwide this year.

However, famine risk will not fully recede until substantive efforts are made to resolve ongoing conflict and improve access, FEWS NET added. The agency said it had increased the number of people it expects to need emergency food aid over the course of 2017.

Its estimate rose to 81 million from the 70 million it predicted in January, due to a series of factors, including below average rainfall in the Horn of Africa. The new estimate was up 20 percent on last year and 70 percent on 2015, it said.

Other causes included access to new data, continuing wars and outbreaks of cholera in Somalia, Yemen and South Sudan.

This file photo taken on March 14, 2017 shows internally displaced families gathering in and outside a hut at a makeshift camp on the outskirts of Baidoa, in the southwestern Bay region of Somalia. (Photo by AFP)

Separately on Wednesday, the head of the International Federation of Red Cross and Red Crescent Societies (IFRC) said the situation in the three countries was rapidly escalating downwards and out of control. Without treatment for malnutrition, more people will fall ill.

Earlier, a UN-backed report said conflict-ridden South Sudan was no longer classified as being in famine although the situation remained critical. In Yemen, war has killed more than 10,000 people, displaced more than 3 million others and ruined much of the impoverished country's infrastructure, pushing nearly half its provinces on the verge of famine, according to the UN.

In Nigeria, some 1.5 million people are on the brink of starvation in the northeast regions, hit by an eight-year insurgency by Boko Haram extremists.

In Somalia, more than 3 million people do not have enough to eat as the country suffers the effects of repeated rain failures and decades of conflict.