The United Nations' Treaty on Prohibition of Nuclear Weapons has entered into force.

However, the main nuclear powers have not signed the accord so far.

The treaty declares that countries ratifying it must never under any circumstances develop, test, produce, manufacture, acquire or stockpile nuclear weapons or other nuclear explosive devices.

Meanwhile, in a statement, the UN Secretary-General Antonio Guterres said the treaty represents strong demonstration of overall support for nuclear disarmament.

He said elimination of nuclear weapons remains the highest disarmament priority of the United Nations.

The UN Chief called on all states to work together to realize this ambition to advance common security and collective safety.