Sanction busters are smuggling 40 tonnes of gold annually out of the Democratic Republic of Congo, a United Nations official has told the BBC.
Dino Mahtani said most of the gold was controlled by rebel groups who use the proceeds to buy arms.
Mr Mahtani, who is due to report to a meeting of the UN Security Council this week, said: "This money helps sustain them [the armed groups] in the field."
Most gold is shipped to Dubai via a neighbouring state, he added.
Mr Mahtani, who co-ordinates UN arms embargo experts, told BBC File on 4: "Recently there was a Congolese Senate report which talked of roughly $1.24bn (£739m) worth of gold or 40 tonnes of material smuggled out on a yearly basis without any customs declaration."
He said the profits of this trade run into several millions of US dollars, which goes back to the armed groups in charge of the illicit trade.
"A lot of this gold is controlled by armed group networks, in particular the FDLR, which is a Rwandan-based rebel group partly composed by members involved in the 1994 genocide and who continue to operate in eastern Congo," he said.
He added that the gold trade is one of the most significant avenues of direct finance for the armed groups.
FIND OUT MORE
Listen to File on 4, BBC Radio 4 2000 GMT, Tuesday 17 November 2009, repeated 1700, Sunday 22 November 2009.
The UN Security Council has had an arms embargo in place in DR Congo for six years following the peace accord between the government and armed groups.
Sanctions were applied to two gold-trading companies that operated out of neighbouring Uganda, but a UN investigator told File on 4 that it would be "quite easy" for people to evade the sanctions because they apply only to the companies and not to named individuals.
Mr Mahtani, is this week to present evidence culled from travel documents, phone records and customs certificates to the Security Council, outlining how DR Congo's gold is traded.
He is convinced that the trade is drawn from a small network of individuals and he added: "When you place companies on a sanctions list and you don't sanction directors of those companies then it's very easy for them to simply change behaviour, set up new front companies and carry on operating.
"So this year we've been looking at some of the directors of these companies and some of the other companies operating in this region and in this trade, and trying to focus on individuals rather than trying to nail companies against a wall, who could easily change names from one day to the next."
The UN Security Council will have to decide whether to impose further sanctions.
File on 4 is on BBC Radio 4 on Tuesday, 17 November, at 2000 GMT, repeated Sunday, 22 November, at 1700. You can also listen via the BBC iPlayerafter broadcast or download the podcast.
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