Evidence of drug factories capable of producing heroin, cocaine and ecstasy has been found in Guinea, the UN says.
The authorities in Conakry alerted the UN after they found large amounts of toxic chemicals in the capital.
The UN says the chemicals give the "best evidence yet" of drug factories, and the organisation is concerned such labs could be widespread in Guinea.
The UN's office on drugs and crime (UNODC) said in a statement it was the first such discovery in West Africa.
The BBC's Alhassan Sillah in Conakry says two businessmen, believed to be close associates of one of the sons of the late President Lansana Conte, have been detained by anti-drug agents in connection with the discoveries.
Of the six sites UN experts inspected, chemicals that could be used to make ecstasy tablets were found on two of them, and solvents commonly used in manufacturing heroin and cocaine were found at others.
"The experts' assessments have confirmed that the quantities and nature of the chemicals found at the locations visited are far in excess of legitimate demands in Guinea," the UNODC statement said.
"The government of Guinea, the UN and Interpol are concerned by the fact that the clandestine production of controlled drugs might be widespread [in Guinea]."
Guinea along with some of its near neighbours has become regarded as a transit point for drugs en route from South America to Europe.
When the military seized power after the death of President Conte at the end of December, they made the fight against drugs a priority.