Vienna  - Columbian cocaine production in 2008 dropped by 28 per cent to the lowest level in a decade, owing to the large-scale eradication of coca plants, the UN drug organization said Friday in Vienna.

However, cultivation of coca rose by 6 per cent in Bolivia and by 4.5 per cent in Peru, the United Nations Office on Drugs and Crime (UNODC) said in its annual survey of the Andean countries.

Some 960 square kilometres of Colombian coca fields were destroyed by hand, 44 per cent more than in 2007. In addition, 1,335 square kilometres were sprayed.

"It means that more coca bush was eradicated in Colombia than was grown in all of Bolivia and Peru," said Antonio Maria Costa, executive director of the Vienna-based UNODC.

The report also showed that the value of coca leaves was falling in Colombia, and that the number of households growing that crop had dropped steeply.

While production fell to 430 tons in that country, increased growing in the other two Andean countries led to higher production figures of 113 tons in Bolivia and 302 tons in Peru.

The UNODC calculates potential production levels based on the amount of cultivated coca.

Costa called for increasing development assistance to farmers in poor regions such as the Yungas in Bolivia, "where coca is the only source of income."

Prices for cocaine went up and drug purity decreased, owing also to a jump in seized drugs in Andean countries in 2008. At the same time, demand shrank in North America and stalled in Western Europe.

"This may also explain why cartels are becoming so violent," the UNODC chief said.(dpa)