United Nations chief Antonio Guterres on Friday warned that the world body is on the brink of financial collapse and could run out of cash by July, as he urged countries to pay their dues.

The UN faces chronic budget problems because some member states do not pay their mandatory contributions in full, while others do not pay on time, forcing it into hiring freezes and cutbacks.

"Either all Member States honor their obligations to pay in full and on time -- or Member States must fundamentally overhaul our financial rules to prevent an imminent financial collapse," Secretary-General Guterres wrote in a letter.