Facing a reported  deficit of $139 million, Guterres said in a letter sent to member states that the United Nations had "never faced such a difficult cash flow situation this early in the calendar year."

As a reminder, U.S. Ambassador Nikki Haley came to the UN in January last year pushing for reform of the world body in a bid to cut costs.

"The inefficiency and overspending of the United Nations are well known. We will no longer let the generosity of the American people be taken advantage of or remain unchecked," she said in December, when the core budget was agreed.

But it appears her words were not heeded as Reuters  reports that only 112 out of 193 member states have so far paid their share of the core budget (compared to 116 at the same time last year). China, France, Russia and Britain - the permanent members of the U.N. Security Council along with the United States - are all paid up for 2018.

Guterres wrote:

"An organization such as ours should not have to suffer repeated brushes with bankruptcy. But surely, the greater pain is felt by those we serve when we cannot, for want of modest funds, answer their call for help."

"We are running out of cash sooner and staying in the red longer."