A UN report has alleged that North Korea has been sending equipment to Syria that could be used to make chemical weapons.
Some 40 previously unreported shipments were made between 2012 and 2017, the report found. Materials included acid-resistant tiles, valves, and pipes.
The report - yet to be released - said N Korean missile specialists had been seen at Syrian weapon-making centers.
The allegations follow new reports of chlorine being used by Syrian forces, which the government denies.
Meanwhile, air strikes were heard in the Eastern Ghouta region outside Damascus as a second daily pause in fighting was due to get underway to allow in relief aid.
Aid was unable to enter the rebel-held region on Tuesday - the first of the five-hour "pauses" in fighting - after clashes continued.
Activists blamed government air and artillery strikes, while Russia said rebels had shelled a "humanitarian corridor" meant to let civilians leave.
North Korea is under international sanctions over its nuclear programme.
But a confidential report, compiled by a US Panel of Experts which assesses North Korea's compliance with UN resolutions, found evidence of illicit supplies sent to Syria.
The report says the items included high-heat, acid-resistant tiles, corrosion-resistant valves, and thermometers.
The Scientific Studies and Research Center (SSRC) - a Syrian government agency - is alleged to have paid North Korea via a number of front companies.
Among the alleged shipments were at least five sent via a Chinese trading firm, Cheng Tong Trading Co Ltd, the report says.
The shipments allegedly contained acid-resistant tiles - which can be used for activities conducted at high temperatures - at a quantity that would cover the area of a large scale industrial project.
While the seized items "do not appear on any control lists", they included "materials that can be used to build bricks for the interior walls of [a] chemical factory", the report noted.