The United Nations could run out of money by the end of the month as it faces a near-unprecedented funding crisis, the secretary-general has warned.

Almost a third of member states have not paid their annual dues leading to a £1.3 billion black hole, António Guterres said in a statement on Tuesday.

The shortage of cash has meant vital staff vacancies have been left empty, travel limited to all but essential journeys and meetings deferred amid attempts to shore up the dwindling reserves. Staff have been warned there may be a default on salaries in November.

Peace-keeping operations, which are paid for from a closed budget, could eventually be scaled back, Mr Guterres indicated.

“The organisation runs the risk of depleting its liquidity reserves by the end of the month and defaulting on payments to staff and vendors,” he said during the shock warning, adding: “Our work and our reforms are at risk.”

He urged the 64 members who have not coughed up – from a total 193 – to do so “urgently and in full”. The appeal came during a committee meeting of the General Assembly on Tuesday morning.