North Korea has not stopped its nuclear and missile programmes in violation of United Nations sanctions, according to a confidential UN report seen by Reuters on Friday.

The six-month report by independent experts monitoring the implementation of UN sanctions was submitted to the Security Council North Korea sanctions committee late on Friday.

"(North Korea) has not stopped its nuclear and missile programmes and continued to defy Security Council resolutions through a massive increase in illicit ship-to-ship transfers of petroleum products, as well as through transfers of coal at sea during 2018," the experts wrote in the 149-page report.

The North Korean mission to the United Nations did not respond to a request for comment on the report.

The UN report said North Korea is cooperating militarily with Syria and has been trying to sell weapons to Yemen's Houthis.