The new findings by the US Office of National Drug Control Policy came after a record year for eradication.
Colombia had 144,000 hectares (556 square miles) cultivated with coca in 2005, compared with 114,100 hectares (440 square miles) found in 2004, the office said.
US officials said the anti-drug strategy they have pursued with Colombia's government - at a cost to US taxpayers of $4 billion since 2000 - has paid off. The cornerstones of the Plan Colombia strategy are interdiction and the aerial eradication of coca fields.
"The obvious question is, 'Is it working?' and I think the answer is obvious," John Walters, the US drug czar, whose office released the survey.
"Where there was no spraying cultivation was up, where spraying is occurring, cultivation is shrinking," Walters said in an interview.
Critics of the anti-drug plan said the survey showed there has been little progress.
"Coca production was not going to be reduced just because fumigation flights spray some fields as long as these farmers don't have any other economic options, except to cut down forests to grow coca somewhere else," said Adam Isacson, a senior policy associate at the Washington-based Centre for International Policy.
Colombia is the global centre of cocaine production and the source of 90% of the cocaine that ends up on US streets, according to the US government.
Colombia is fighting a decades-old
The billions of dollars made from the cocaine industry feed Colombia's long-running guerrilla conflict that pits leftist rebels against far-right paramilitaries and the government.
Walters said the anti-drug plan was having an impact on the country's conflict.
"Money from cocaine supports drug-traffickers, supports armed groups that are terrorists, supports the destabilisation of the Colombian government," Walters said. "All those thing are getting better, the terrorist groups are weaker ... they are receiving less money, murders are down, kidnappings are down."
Last year, Colombia eradicated a record 170,000 hectares (656 square miles) of coca, mainly by aerial fumigation with the herbicide glyphosate, up from 137,000 hectares (529 square miles) in 2004.
The increase in the land surveyed by the US government using satellite imagery highlights a new trend: the dispersal of coca throughout this South American nation. Just five years ago, almost all of Colombia's coca was found in southern provinces close to the Ecuadorean border. Now coca can be found across this country, twice the size of France, with reports of the crop an hour's drive from the Colombian capital of Bogota.
The new survey figures for coca cultivation could be an underestimate, said John Walsh, a drug policy expert at the Washington Office on Latin America (WOLA), which has criticised the anti-drugs strategy.
"The figures should be taken with a grain of salt, since they in all likelihood significantly understate the true extent of coca cultivation and cocaine production," Walsh said.