Almost $9-billion was illicitly siphoned out of Zambia, Africa's top copper producer over the last decade, according to a report by a U.S. anti-graft watchdog, which highlights how resource wealth is often squandered in the developing world.
The amount is almost half the size of Zambia's current gross domestic product and much of the money would have been channelled to offshore banks and tax havens, draining one of the world's poorest countries of badly needed capital.
The Zambian government said the report was in line with its own findings and vowed to crack down on culprits.
The report by U.S.-based anti-graft watchdog Global Financial Integrity (GFI) said the southern African nation lost $8.8-billion to capital flight between 2001 and 2010.
"Of that, $4.9-billion can be attributed to trade mis-invoicing, which is a type of trade fraud used by commercial importers and exporters around the world," GFI economist Sarah Freitas said.
The way this typically works is that an importer pretends to pay more to foreigners than they actually spend, with the difference put discreetly into banks or other assets abroad.
Major commodity producers seem especially susceptible to these trends because of the often-opaque nature of resources industries.
Last year, calculations provided to Reuters by GFI estimated that Zambia's neighbour Angola, Africa's second-largest oil producer, had lost almost $6-billion to capital flight in 2009.
Aside from trade mis-invoicing, money can also be spirited illegally offshore via official corruption or criminal activities, which can be traced through balance of payments data.
GFI uses the International Monetary Fund's Direction of Trade statistics for its calculations.
Zambian government officials have long maintained copper producers in the country have not been paying their share of taxes.
"These revelations are in line with what we have always been saying with regard to tax avoidance and income leakages in general," Finance Deputy Minister Miles Sampa said of the GFI report.
"The onus is on us … to put and implement proper monitoring measures. Where the law is being broken our law enforcement agencies will move in and arrest the culprits so that they can be punished."
Former Zambian mines minister Wylbur Simuusa said earlier this year that the government of populist President Michael Sata believed it was owed up to $1-billion in back taxes from mining houses in the country.
Transparency questions have also been raised in the past about the accuracy of Zambia's copper export data.
GFI announced its findings on Zambia ahead of the release on Tuesday of its full report measuring illicit financial flows out of 150 developing countries and emerging economies in the last decade.