The United Nations has an overall annual operating budget of several billion dollars, covering everything from humanitarian work to disarmament, but right now, it's just trying to make sure its employees get paid after this month.

How did the world body end up more than $200 million (over R3bn) in the red?

The answer: member states who have not paid their expected contributions, including the United States.

On Tuesday, Secretary-General Antonio Guterres warned of the "worst cash crisis facing the United Nations in nearly a decade".

He cautioned the UN "runs the risk of depleting its liquidity reserves by the end of the month and defaulting on payments to staff and vendors."

Not paying up

Several member states are behind in their dues payments. The UN will not publicly identify those countries, but sources told AFP the main culprits are the United States, Brazil, Argentina, Mexico and Iran.

In all, 64 countries owe money to the UN. Also on the list of budget delinquents are Venezuela, North Korea, South Korea, the Democratic Republic of Congo, Israel and Saudi Arabia.

The last country to have paid up is war-wracked Syria, UN spokesman Stephane Dujarric said Tuesday at his daily press conference.

In a letter sent on Monday to the 37 000 employees at the UN secretariat, which was obtained by AFP, Guterres said the UN had a deficit of $230m as of the end of September.

On Tuesday, he indicated that if the world body had not taken the initiative to cut spending since the start of the year, the hole would have been even bigger in October - possibly $600m (over R9bn) - and could have affected last month's General Assembly attended by world leaders.

Travel cuts

In his statement on Tuesday, Guterres thanked the 129 member states who have paid up "and urged those who have not paid to do so urgently and in full."

To limit expenditures from now until year's end, the UN chief has raised the possibility of postponing conferences and meetings, limiting all but essential official travel, and reducing services.

A UN official speaking on condition of anonymity said Guterres had raised the budget issues with member states as early as this past spring, asking them to pay up, but they refused.

Not including what it pays for peacekeeping operations, the UN's operating budget for 2018-2019 is close to $5.4 billion (R84bn), with the United States contributing 22%.

The portion still owed? Nearly $1.4 billion (R21bn).

Washington is also the largest contributor to the UN peacekeeping tab.

President Donald Trump's administration has taken a hard line on UN funding, cutting contributions and pushing for cost-saving reforms.