The report also said that the illicit technology transfers had "trans-shipment through a neighbouring third country." That country was China, several diplomats told Reuters on condition of anonymity.
The report was submitted to the UN Security Council by a UN panel of experts, a group that monitors compliance with UN sanctions imposed on North Korea after it conducted two nuclear tests in 2006 and 2009.
The UN sanctions included a ban on trade in nuclear and missile technology with North Korea, as well as an arms embargo. The UN measures also banned trade with a number of North Korean firms and called for asset freezes and travel bans on a number of North Korean individuals.
"Prohibited ballistic missile-related items are suspected to have been transferred between the Democratic People's Republic of Korea [North Korea] and the Islamic Republic of Iran on regular scheduled flights of Air Koryo and Iran Air," the report said.
"For the shipment of cargo, like arms and related materiel, whose illicit nature would become apparent on any cursory physical inspection, [North] Korea seems to prefer chartered cargo flights," it said.
It added that the aircraft tended to fly "from or to air cargo hubs which lack the kind of monitoring and security to which passenger terminals and flights are now subject."