Mr Morales is a former coca farmer
President Evo Morales has rejected a US request to fly anti-narcotics missions over Bolivia, state media has reported.
The Bolivian Information Agency said Mr Morales told officials to deny a request from the US Drug Enforcement Agency (DEA) for a surveillance flight.
It is the latest in a series of standoffs between the two countries.
Last month, the US government added Bolivia to a list of countries that it said had failed in their counter-narcotics obligations.
Also last month, Mr Morales expelled the US ambassador, accusing him of supporting opposition protests.
Washington denied the claim, and promptly expelled the Bolivian ambassador.
Last week, the US took initial steps to suspend trade benefits for Bolivia over what it said was the country's poor co-operation in fighting drug trafficking.
"Two days ago I received a letter... asking a government institution for permission to fly over national territory," the agency quoted Mr Morales as saying.
"I want to say publicly to our authorities: They are not authorised to give permission so that the DEA can fly over Bolivian territory," he said.
Coca is widely used by Bolivian Indians
Mr Morales, a former coca farmer, rose to power leading protests against US drug policy.
He has been under political pressure at home as violent protests have been staged in eastern parts of the country over his decision to hold a referendum on a new constitution in December.
Bolivia is the world's third largest producer of coca, the base ingredient in cocaine.
The coca leaf is the main ingredient for cocaine, but it is also widely used by Bolivian Indians, who chew it for its medicinal properties.