Countries will be barred from trading diamonds internationally if they don’t help stop illegal trafficking of the gems that finance deadly wars across Africa, representatives of 56 countries warned Wednesday, The Associated Press reports.

At the close of a three-day conference this week, the group said countries must implement a system by July 31 to stop the flow of the illicit jewels, the AP reports.

“The most effective sanction is total isolation from the diamond industry,” Abbey Chikane, chairman of the Kimberley Process—a meeting of governments, diamond industry officials and human rights groups working to end the illegal trade of diamonds.

The group has not approved the diamond certification process for 14 countries, including Angola and Congo—where the diamond trade has helped fund years of wars.

According to the group, diamond-producing and diamond-trading nations must issue certificates to confirm the origins of rough diamonds. Previously, diamond trading required a certificate stating what country last exported the diamond, not where it was mined.

Officials say the certification is an important step to begin cracking down on the illegal trade, which they concede is a massive effort. Gems worth millions of dollars can be smuggled across borders in a single shirt pocket.

Diamond industry officials began talks in Kimberley, South Africa, in 2000 on how to stop the illegal trade.

Now known as the Kimberley Process, the group meets annually.

JCK