Bolivia's government has decided to renounce the United Nations' anti-drug convention because it classifies coca leaf as an illegal drug, the Foreign Ministry said.
The decision comes after a proposal by President Evo Morales to remove language obliging countries that have signed the convention to ban the chewing of coca leaves was rejected following US objections.
Bolivian officials contend that coca leaf in its natural form is not a narcotic and forms an age-old part of Andean culture. Morales is a former coca growers' union leader who has campaigned for the leaf's traditional uses.
Coca is a mild stimulant with high religious and social value in the Andean region. But while it fights hunger and alleviates altitude sickness, it is also the raw material of cocaine.
The Bolivian Foreign Ministry confirmed that its decision was presented to Ban Ki-moon, the UN Secretary-General, in New York.
The Andean nation plans to rejoin the 1961 Single Convention on Narcotic Drugs, but noting its objection to the penalisation of coca chewing.
US officials have said they are concerned that Bolivia's proposal would weaken the integrity of the UN convention.