Military police are investigating claims that British and Canadian soldiers trafficked heroin from Afghanistan.
The British Ministry of Defence says it's aware of unsubstantiated claims that troops are using military aircraft to ship the drug out of the country.
The inquiry is focusing on British and Canadian service personnel at airports in Camp Bastion and Kandahar, the BBC reports.
Security has been tightened, with additional sniffer dogs being used as part of a crackdown at the bases.
Afghanistan is the source of 90% of the world's opium.