North Korean leader Kim Jong Un gives field guidance at the Pyongyang Pharmaceutical Factory, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang January 25, 2018.
The monitors added that they had investigated an ongoing ballistic cooperation between Syria and Myanmar, which also includes over 40 unreported North Korean exports between 2012 and 2017 to Syria's Scientific Studies and Research Centre, Reuters reported.
The report also revealed that there was evidence of military co-operation with Syria and Myanmar.
According to the document obtained by Reuters, a group of independent United Nations monitors is also accusing Pyongyang of providing weapons to Syria and Myanmar. It banned all exports of coal by North Korea on Aug 5, 2017.
The report says the North used trans-shipment through third countries and fraudulent documentation to obscure the origin of the coal. In 2013, Panamanian forces confiscated a North Korea-flagged ship after undeclared Cuban weapons and fighter jets from the Soviet era were found under sacks of sugar.
A confidential report prepared by independent United Nations monitors and seen by Reuters on Friday also states North Korea supplied weapons-including ballistic missile systems-to Syria and Myanmar.
A member state, which also remained unnamed, notified the panel that Myanmar had received "ballistic missile systems from [North Korea] in addition to a range of conventional weapons, including multiple rocket launches and surface-to-air missiles".
Shortages would lead to serious humanitarian problems, he said, adding: "Official representatives of Pyongyang have made it clear that a blockade would be interpreted by North Korea as a declaration of war, with all the subsequent consequences".
Coal shipments were delivered to China, Malaysia, South Korea, Russia and Vietnam by ship using "a combination of multiple evasion techniques, routes and deceptive tactics", said the report. The coal cargo "would constitute a violation of the resolution, if confirmed".
"We must put an end to illicit ship-to-ship transfers that undermine United Nations sanctions", he said.
The United States led the push for tough economic sanctions after North Korea's sixth nuclear test and a series of ballistic missile launches that raised fears that the USA mainland could soon be within range.
While Syria claimed North-Korean experts were involved in sport, Myanmar denied any connection.