WASHINGTON—North Korea shipped 50 tons of supplies to Syria for use in building what is suspected to be an industrial-scale chemical weapons factory, according to intelligence information cited in a confidential United Nations report.

A Chinese trading firm working on behalf of Pyongyang made five shipments in late 2016 and early 2017 of high-heat, acid-resistant tiles, stainless-steel pipes and valves to Damascus, the report said, citing them as evidence that Syrian President Bashar al-Assad is paying North Korea to help…