Meanwhile, US Secretary of State Mike Pompeo has suggested Kim Jong Un "remains committed to denuclearisation"
North Korea has not stopped its nuclear and missile programmes, according to a leaked report for the UN Security Council.
The confidential report - which was prepared by a panel of independent experts - was seen by a number of news agencies, and reportedly suggests North Korea is violating international sanctions.
As quoted by Reuters, the report states: "[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 country is also accused of violating a textile ban by exporting more than $100 million in goods to countries including China, Mexico and Turkey between October 2017 and March 2018.
Meanwhile, US Secretary of State Mike Pompeo has insisted that North Korea is 'closer to denuclearisation' since the historic US-North Korea summit in June.
Mr Pompeo was speaking in Singapore as he met with counterparts from Singapore, Australia, Japan and South Korea.
The trip comes almost two months after Donald Trump and Kim Jong Un met in the city-state.
Earlier this week, President Trump praised the North Korean leader for 'keeping his word' and returning remains of US troops killed during the Korean War.
Speaking to Channel NewsAsia yesterday, Mr Pompeo said: "We said we are prepared to improve the relationship between our two countries and offer a brighter future for North Korea. We’re still intent upon that.
"We’re thrilled that North Korea fulfilled its commitment by beginning the process of returning the remains of American servicemen this past week. We hope that process will continue. And we’re confident that Chairman Kim remains committed to denuclearisation. The world is counting on it."
However, he also stressed that "sanctions must remain in place" until denuclearisation is achieved.