Billions of dollars in funding is needed to help millions of people facing largely man-made disasters in Yemen, South Sudan, Somalia and Nigeria, the United Nations humanitarian chief said on Friday

"We are facing the largest humanitarian crisis since the creation of the United Nations," UN humanitarian chief Stephen O'Brien warned the U.N. Security Council as he detailed the situation in the conflict-hit countries.

"To be precise we need 4.4 billion dollars by July, and that's a detailed cost, not a negotiating number," he said. In addition to funds, he urged for aid groups to be guaranteed "safe and unimpeded access" to deliver humanitarian aid.

Yemen hit hardest

O'Brien noted that the largest humanitarian crisis is currently in Yemen where 18.8 million people - two-thirds of the population - need aid. Another seven million people are hungry and do not know where their next meal will come from.

The Arab world's poorest nation has been engulfed in conflict, with over 7,400 people dead and 40,000 wounded since March 2015. 

During a recent visit to Yemen, O'Brien said he met with senior leaders of the government and Houthi rebels who both promised access for humanitarian aid.

"Yet all parties to the conflict are arbitrarily denying sustained humanitarian access and politicize aid," he said, warning if that behavior doesn't change now "they must be held accountable for the inevitable famine, unnecessary deaths and associated amplification in suffering that will follow."

Children particularly at risk

In Somalia, over half of the population - 6.2 million people - are in need of aid, including 2.9 million who are at risk of famine and need immediate help to "save or sustain their lives," the UN humanitarian chief said.

Around one million children under the age of five will be "acutely malnourished" by the end of the year, O'Brien added.

Last month, a UN humanitarian coordinator said that malnutrition in northeast Nigeria was so prevalent that some communities had lost all of their toddlers.

'It is all preventable'

In South Sudan, a country which has beenravaged by a three-year civil war, aid workers have been killed and supplies have been looted by "armed actors," O'Brien said. He also noted that the famine threatening the world's newest nation is "man-made."

He urged for the Security Council and the international community to quickly intervene.

"It is all preventable," he said. "It is possible to avert this crisis, to avert these famines, to avert these looming human catastrophes."

Without the assistance, however, "many people will predictably die from hunger, livelihoods will be lost, and political gains that have been hard-won over the last few years will be reversed."

rs/ rc (AP, dpa)