KABUL, Afghanistan — Driven by soaring opium prices, farmers are expected to plant poppies at a sharply higher rate in parts of Afghanistan that were previously poppy free, the United Nations said Monday in its annual winter survey of poppy cultivation patterns in this country, the world’s leading opium purveyor.

Poppy planting is expected to be down slightly over all because of modest decreases in the southern provinces of Helmand and Kandahar, the country’s most productive opium regions. The provinces continue to produce, but officials expected significant increases in the north and northeast provinces of Badakhshan, Baghlan and Faryab, as well as the southern and western provinces of Herat, Kapisa and Ghor.

Baghlan, Faryab, Kapisa and Ghor were all poppy free in 2010. Sixteen of the country’s 34 provinces are expected to remain poppy free, a decrease from 20 last year. The drop represents what United Nations officials called a disturbing reversal in efforts to reduce opium production, a major revenue source for the Taliban insurgency.

Prices for dry opium jumped 306 percent this year, to $281 a kilogram from $69 last year. It was the second consecutive year of sharp increases, which the report attributed to a blight that destroyed nearly half of last year’s crop.