Narino, in the south, continues to have the highest density of coca plants
The area of land planted with coca - the raw ingredient for cocaine - in Colombia has fallen by 25%, a UN report has said.
The land under coca cultivation is now about a third of that in 2001, says the UN Office on Drugs and Crime (UNODC).While coca areas fell nationwide, they rose in three provinces plagued by rebels and drug gangs.
Colombia is one the world's top three cocaine producers and has made the war on drugs one of its main priorities.
Prevention v eradication The annual report by the UN's Integrated Illicit Crops Monitoring System says that the land planted with coca bushes has dropped from 64,000 hectares in 2011 to 48,000 hectares in 2012, the lowest figure since monitoring started in Colombia more than a decade ago.
Analysts say the fall in coca production suggests illegal groups which have so far financed themselves through drug trafficking may increasingly be moving into illegal gold and emerald mining, both of which have been increasing in Colombia.
The groups take advantage of the fact that, unlike coca or cocaine, gold and emeralds are legal to transport and sell.
Mine field But the head of Colombia's counter-narcotics police, Gen Luis Alberto Perez, told us that the UN figures showed that their strategy to focus on the worst-affected areas had worked.
Drug gangs and Farc rebels turn coca leaves into cocaine to finance themselves
He said that even though the police had eradicated less coca
than in previous years, the force had increased its presence in those
regions where most of the coca was grown, preventing people from
planting coca bushes in the first place.He also praised the government's social programmes, which aim to convince farmers to switch from growing coca to legal crops.
The UNODC report, which uses satellite imagery to map areas planted with coca, says that there was an increase in coca plantations in three provinces: Norte de Santander, Choco and Caqueta.
According to Gen Perez, police activity in these three provinces was hampered by left-wing Farc rebels and drug gangs.
The general says an increased use of landmines by these groups means that eradication workers cannot pull out the plants by hand without the risk of stepping on a mine.
Border trouble The border regions have the highest density of coca plants, with the southern town of Tumaco again topping the list.
Colombia agreed to the exclusion zone after Ecuador brought a complaint against its neighbour at the International Court of Justice in 2008 saying its territory was being poisoned by the spraying.
According to UN figures released earlier this week, coca growing also decreased in Bolivia.
The UNODC said coca cultivation had dropped by 7% between 2011 and 2012 to 25,300 hectares.
Bolivia is, along with Colombia and Peru, among the world's top three producers of cocaine.
The figures for Peru are expected to be released over the next weeks