North Korea has been sending equipment to Syria that could be used to make chemical weapons.
A UN report said some 40 previously unreported shipments were made between 2012 and 2017.
Materials included acid-resistant tiles, valves and pipes.
The report – yet to be released – said North Korean missile specialists had been seen at Syrian weapon-making centres.
The allegations follow new reports of chlorine being used by Syrian forces, which the government denies.
A second daily pause in fighting in the Eastern Ghouta region outside Damascus is due to begin, to allow in relief aid.