Revenue from opium production in Afghanistan soared by 133 percent last year to about $1.4 billion, or about one-tenth of the country's GDP, according to a United Nations report received Friday.

The U.N. Office on Drugs and Crime said the price rise was due to a plant disease that wiped out much of the opium crop in 2010. Although yields returned to pre-blight levels in 2011, the prices have remained high, the survey said.

Definitive statistics are hard to obtain in Afghanistan, but the survey said the value of the crop may now be the equivalent of nine percent of the country's GDP.