The UN chief has told states that the organisation is at risk of "imminent financial collapse", citing unpaid fees and a budget rule that forces the global body to return unspent money, according to a letter seen by Reuters on Friday.
"The crisis is deepening, threatening programme delivery and risking financial collapse. And the situation will deteriorate further in the near future," United Nations Secretary-General Antonio Guterres wrote in a letter to ambassadors dated 28 January.
The UN is facing a cash crisis as the world body's largest contributor, the United States, has slashed voluntary funding to UN agencies and refused to make mandatory payments to the UN's regular and peacekeeping budgets.
In the letter, Guterres said "decisions not to honour assessed contributions that finance a significant share of the approved regular budget have now been formally announced."
It was not immediately clear which state or states he was referring to and a UN spokesperson was not immediately available for comment.
"Either all Member States honour their obligations to pay in full and on time, or Member States must fundamentally overhaul our financial rules to prevent an imminent financial collapse," he said, warning that cash could run out by July.
