WASHINGTON, June 4 (Reuters) - More than 387,900 acres (157,000 hectares) of coca were detected in Colombia in 2006, an increase of 32,120 acres (13,000 hectares) from the previous year, the White House anti-drug office said on Monday.

The Office of National Drug Control Policy (ONDCP) said the area surveyed in 2006 was 19 percent larger than in 2005 and that almost all of the increase in coca cultivation was found in the newly surveyed areas.

However, statistically there was no change in the amount of coca being grown between 2005 and 2006, the agency said.

"Because they had not been previously surveyed, it is not possible to know with certainty if the coca found in the areas is in fact newly planted and had not been producing for a period of time," the ONDCP said in a statement.

"Rapid crop reconstitution, a move to smaller plots and the discovery of previously unsurveyed coca growing areas, have posed major challenges to the techniques and methodologies used to understand Colombia's coca cultivation and cocaine output," the statement said.

Colombia has received around $4 billion in U.S aid since 2000 to help fight traffickers and the Revolutionary Armed Forces of Colombia, or FARC, accused by U.S. and Colombian officials of using the drug trade to finance Latin America's longest insurgency.

Colombia says the U.S.-backed fumigation program is the only way it can counter coca production in remote areas where guerrillas are still fighting government forces.

Officials estimate the Andean country still produces around 600 tonnes of cocaine a year, most of which is shipped to the United States and Europe.

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