North Korea earned nearly $200m (£141m) last year by exporting banned commodities in breach of international sanctions, a UN report says.
The report by a panel of experts said several countries including China, Russia and Malaysia had failed to stop the illegal exports.
It said there was evidence of military co-operation with Syria and Myanmar.
Pyongyang is subject to sanctions from the US, UN and EU over its nuclear and ballistic missile programmes.
But the report, which was submitted to the UN Security Council, said the North "continued to export almost all the commodities prohibited in the resolutions… between January and September 2017".
The report said several unnamed multinational oil companies were being investigated for their alleged role in supplying petroleum products to North Korea.
It said shipments of coal had been delivered to China, Malaysia, South Korea, Russia and Vietnam in breach of sanctions using "a combination of multiple evasion techniques, routes and deceptive tactics".
Monitors found that Myanmar and Syria continued to co-operate with North Korea's main arms exporter, Komid, despite it being on a UN sanctions blacklist.
The report said there was evidence that the North was helping Syria to develop chemical weapons and providing ballistic missiles to Myanmar.
Syrian officials had told the monitors that the only North Korean experts on its territory were involved in sports.
Myanmar's ambassador to the UN said the country had no arms relationship with North Korea.