Eradication by hand is hard but in some areas the only way to do it
Colombia's cultivation of coca, the raw material for cocaine, jumped last year by 27%, a United Nations report says.
The UN's office on drugs and crime (UNODC) says the increase is "a surprise and a shock" given Colombia's efforts to destroy coca crops.
The US has also spent millions of dollars to help Colombia, the biggest cocaine producer, eradicate coca.
The main reason for the rise is that growers are managing to replant the crop quickly, the UN says.
The 2007 Andean coca survey shows that the total area of land under coca cultivation in Bolivia, Colombia and Peru in 2007 was 181,600 hectares - a 16% increase on 2006 and the highest level since 2001.
The biggest rise was in Colombia. Bolivia and Peru saw much smaller increases - 5% and 4% respectively.
COCA AND COCAINE
Colombia: 99,000 hectares
Peru: 53,7900 ha
"The increase in coca cultivation is a surprise and shock: a surprise because it comes at a time when the Colombian government is trying to hard to eradicate coca; a shock because of the magnitude of cultivation," said Antonio Maria Costa, head of the UNODC.
The UNODC report points out that almost half of cocaine production in Colombia is in just 5% of the country.
"Just like in Afghanistan, where most of the opium is grown in provinces with a heavy Taleban presence, in Colombia most coca is grown in areas controlled by insurgents," said Mr Costa.
"In the future, with the Farc (Colombia's biggest rebel group) in disarray, it may become easier to control coca cultivation."
Despite the rise in the coca crop, cocaine production in the Andean region remained almost unchanged in 2007, up from 984 tonnes to 994.
The UNODC says this is because farmers are having to move into smaller, more dispersed locations to avoid eradication operations and aerial spraying.
Colombia gets major US funding to tackle the illegal drugs trade
Since 2000, Washington has spent some $5bn (£2.5bn) to fight drug trafficking, train the Colombian army to battle insurgents and improve the institutions of government.
However, there has been criticism, including from some Democrats in the US Congress, that the aid is targeted mainly at the military, rather than for social projects to help farmers switch to other crops.
Regarding Bolivia, the UNODC says the main coca-growing regions include La Asunta and the Yungas de La Paz where investment in development has been scarce.
Rising prices for crops such as coffee, palm oil and cocoa which are grown under alterative development programmes, are convincing a growing number of farmers not to replant coca, the UNODC says.