Gold production in Democratic Republic of Congo continues to be systematically underreported while tonnes of the precious metal is smuggled into global supply chains through its eastern neighbours, a United Nations report has found.

The countries along Congo's eastern border have long been conduits for gold worth billions of dollars mined using rudimentary means by so-called "artisanal" miners.

Difficult to trace, trade in the precious metal has fueled regional wars, funded rebel fighters and led to UN sanctions on traders involved in a bid to staunch the flow.

North Kivu, South Kivu and Ituri provinces reported official production of just over 60kg of artisanal gold in 2019, yet exported a total of just over 73 kg, the UN Group of Experts on the Congo found in its annual report.

The group estimated that at least 1.1 t of gold were smuggled out of Ituri province alone in 2019. That would have earned the government up to $1.88-million in taxes had it been legally exported.

Across all gold-producing provinces the loss is likely much greater. Artisanal miners in Congo produce 15 t to 22 t of gold a year, Germany's Federal Institute for Geosciences and Natural Resources has estimated.

"The country remained one of the Great Lakes region's largest artisanal gold producers, and yet one of its smallest official exporters," the Group of Experts wrote.

Asked by Reuters about the report, Congo's Mines Minister, Willy Kitobo Samsoni, said he could not immediately share his figures on mineral smuggling from the east of the country.

The UN experts also found that Uganda and other neighbouring countries export far more gold than they produce, suggesting they might still be staging posts for smuggled Congolese gold.

More than 95% of gold exports from Uganda in 2019, which totaled just over 25 t, were not of Ugandan origin, the group estimated, based on 2018 production and 2019 export data.

Uganda's gold exports more than doubled in 2019 compared with the previous year, central bank data showed in March.

Uganda's Energy Minister did not immediately respond to a request for comment on the report.

Smugglers told the Group of Experts that Kampala was a main trading hub for gold from Ituri. Smuggled gold from South Kivu went to Burundi, Rwanda, the United Arab Emirates, and Tanzania, the report added.