"Government policies related to zero coca, and strict verification procedures, take a long time and limit the state's ability to work with communities in transitioning from a coca economy to a legal economy," a recent US Agency for International Development (USAID) report said.

"When security and coca eradication are not synchronised with the arrival of socio-economic projects, the mood of a community can quickly become hostile."

A new book, Shooting Up: Counter-insurgency and the War on Drugs, by the respected Brookings Institution scholar Vanda Felbab-Brown, says eradication campaigns in Afghanistan and Colombia have left drug production unaffected but alienated locals, gifting political capital to insurgents.

Plan Colombia, the military-heavy US aid programme, has had significant success in helping the country's security forces push Revolutionary Armed Forces of Colombia (Farc) guerrillas out of cities and deep into the jungle.