report obtained by Reuters.
The report said the illicit technology transfers had "trans-shipment through a neighboring third country." That country was China, several Diplomats told Reuters on condition of anonymity.
The report will likely deepen suspicions about North Korean cooperation with Iran and heighten concerns about China's commitment to enforcing the sanctions against Tehran and Pyongyang due to their nuclear programs, envoys told Reuters.
The report was submitted on Friday to the Security Council by a UN Panel of Experts, a group that monitors compliance with UN sanctions imposed on Pyongyang after it conducted 2 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. They also banned trade with a number of North Korean firms and called for asset freezes and travel bans on some 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."
Several Security Council Diplomats said China was unhappy about the report and would likely not agree to release it to the public. At the moment, only the 15 Council Members have official access to the document.
One of the experts on the panel is from China and Diplomats said he never endorsed the report, which was delivered to the Security Council on Friday. His refusal to endorse the report delayed its submission for around 24 hours, Diplomats said.
Beijing has prevented the publication of expert panel reports on North Korea and Sudan in the past. Earlier this week, Russia took similar steps to suppress an equally damning UN expert panel report on Iran.
The spokesman for China's UN mission was not available for comment. Further evidence of Iran's cooperation with North Korea on missile technology came during a military parade in October 2010, the report said, when North Korea displayed a new warhead for its Nodong missile.
The warhead had "a strong design similarity with the Iranian Shahab-3 triconic warhead."