While most of the diamonds on the world market are guaranteed to be legitimate, many of those that are not end up mixed in with the rest, Deutsche Welle reported.

"The problem is that conflict diamonds very rarely come directly from the source country," said Annie Dunnebacke of the Global Witness' Conflict Diamond Campaign. "Rough and uncut diamonds can easily be smuggled over porous borders from places like the Ivory Coast and can obtain a Kimberley Process certificate from another country before being shipped to Europe."

The Kimberly Process was adopted in 2002 out of concern that "blood diamonds" were funding rebel groups in African countries. Under the process, rough diamonds are sealed into containers and supplied with forgery-resistant certificates with unique serial numbers.

Almost 40 percent of rough diamonds, assessed by value, are sent to Europe -- most to the diamond-cutting center of Antwerp, Belgium.