By Mark Doyle BBC correspondent

Statistical anomalies suggest the Central African Republic is being used to smuggle gems from rebel-held areas of neighbouring Democratic Republic of Congo, a new report says.

Trading in diamonds used to finance conflict is in violation of international guidelines which came into force at the beginning of this year.

Conflict gems are mixed with CAR diamonds

But the guidelines for an international certification scheme tracing the origin of rough diamonds are not independently monitored.

The report highlighting the situation in central Africa is part of a campaign by the lobby group Partnership Africa-Canada to strengthen the guidelines.

Discrepancy

The quantity of diamonds Belgium imports annually from the CAR is much higher than the African state officially exports, according to the report.

"The Central African Republic exports officially $60m in diamonds. Belgium imports two to three times that," Brussels-based researcher Chris Dietrich says.

"Last year it was only $100m but the year before it was $160m."

The Central African Republic exports officially $60m in diamonds. Belgium imports two to three times that Chris Dietrich

The CAR Government says the explanation is that traders in diamonds from all over the world wrongly declare their origin as the CAR for tax or legal reasons.

But the report notes links between arms dealers and diamond traders in both countries.

All this reveals the strong likelihood that conflict diamonds from the DRC are being laundered through the CAR, it says.

The report urges the Central African Government to stop the trafficking and implement credible, independent reviews of the situation.