VIENNA (AFP) - The United Nations and Bogota signed a major pact on Friday (Nov 3) to uproot Colombia's booming cocaine business, as part of peace efforts between the government and drug trade-controlling rebels.

The deal worth US$315 million (S$430 million) aims to wean farmers off growing coca - the raw material for cocaine - by replacing it with safer crops such as coffee and cacao.

The Vienna-based Office on Drugs and Crime (UNODC) said it was one of the most ambitious initiatives to date to free rural communities from the clutches of drug dealers.

Colombia is ranked by the United Nations as the world's biggest producer of coca.

Its growing area rose by a staggering 52 per cent to 361,000 acres last year.

"This historical agreement is a unique opportunity to turn the tide against Colombia's coca cultivation and help farmers embrace alternative development," UNODC head Yury Fedotov said in a statement.

Colombia's special post-conflict envoy Rafael Pardo Rueda hailed the project as "fundamental" for the implementation of a historic peace deal sealed in June between Bogota and the Revolutionary Armed Forces of Colombia (Farc).

'NOT AN EASY TASK'

For decades the drug trade funded the Farc, the country's largest rebel group, which controlled key regions where coca leaf and cocaine production flourished.

The organisation was formed in 1964 to fight for land rights and to protect rural communities.

The conflict drew in leftist guerrillas, right-wing paramilitary groups and state forces and has left 260,000 people dead, more than 60,000 missing and seven million displaced.

But after lengthy negotiations, the Farc this summer agreed to disarm and help weed out coca by persuading farmers to switch to other forms of agriculture.

In exchange, the UN established a new mission in Colombia in July to help thousands of former Farc combatants return to mainstream society.

However progress has been slow as ex-rebels struggle to reintegrate, leaving them tempted to join other dissident groups, keep their weapons, and traffic drugs.

As a result, many villagers still face threats from armed dissidents to keep growing coca.

"Reduction of coca crop area is not an easy task in terms of administrative or logistical procedures, but it's also not an easy task in terms of it being a reduction of an illegal rent to an illegal group," Rueda, who is also Colombia's labour minister, told AFP.

In addition, eradication teams have to navigate around numerous landmines planted to protect the coca plantations.

But Bogota is hopeful that the UN-backed initiative will blow a hole in the drug trade by offering Colombia's 120,000 coca-growing families incentives to go legal.

Farmers earn around US$300 a month per hectare of coca but need to give a big cut to the dealers, Rueda said.

Colombia is now offering them the same amount, which they get to keep in full.

The goal is to get rid of 100,000 hectares by next year - half by forced eradication and half by the voluntary substitution programme.