European timber companies have helped fund the war in the Central African Republic through lucrative deals with militia groups, campaign group Global Witness alleges in a new report.
Traders in France and Germany paid more than $4m (£2.5m) to rebel groups accused of war crimes, the report says.
It accuses the EU of failing to stop imports of illegal timber to Europe.
Thousands of people have been killed in the conflict which followed a coup by the Seleka rebel group in March 2013.