BRUSSELS, Belgium — Bolivia needs urgent international help to stop farmers from turning to coca production as a political crisis distracts efforts to combat drugs, the head of the U.N. drugs office said yesterday.

The impoverished Andean nation is the world's third-largest producer of coca, which is used to make cocaine, and has seen a steady rise in coca planting in the past five years.

South America's cocaine output rose by 2 percent last year, bucking a five-year downward trend as increases in Peru and Bolivia outpaced Colombia's clampdown on coca cultivation, according to the annual survey from the United Nations Office on Drugs and Crime (UNODC).

"We are very concerned about the situation in Bolivia," Antonio Maria Costa, executive director of UNODC, said in Brussels.

Weeks of crippling protests by indigenous groups, laborers and miners forced President Carlos Mesa to resign last week, the country's second leader in two years to be ousted by protests over who should own Bolivia's gas reserves. His successor, Eduardo Rodríguez, has promised early elections.

Costa said experiences in countries such as Afghanistan had shown that political instability frequently led to increased cultivation of illegal crops as authorities turn their attention to tackling the unrest and drugs policy becomes less effective.