UNITED NATIONS - UN Secretary-General Antonio Guterres has sent a letter to UN member states, expressing concerns over "enormous challenges" posed by COVID-19 and financial pressure of UN operations, his spokesperson Stephane Dujarric said here on Thursday.

The world organization ended 2019 with arrears of $711 million, the highest level for a decade and a 34 percent increase compared to 2018, Guterres said, adding that the pressure comes from continued financial constraints.

There is a sharp decline of 42 percent in the payment of assessments by member states, compared to 50 percent in earlier years, he added.

The secretary-general also said in his letter that he is directing managers to temporarily suspend all hiring for regular budget operations and to further scale down non-post expenses to ensure timely payments to staff and vendors.