Afghanistan's criminal underworld has compromised key government officials who protect drug traffickers, allowing a flourishing opium trade that will not be stamped out for a generation, an ominous U.N. report released Tuesday said.

The fight against opium production has so far achieved only limited success, mostly because of corruption, the joint report from the World Bank and the United Nations Office on Drugs and Crime said.

The findings show a "probability of high-level (government) involvement" in drugs, said Doris Buddenberg, the UNODC's Afghanistan representative and co-editor of the report.

The report in particular presented a strong indictment of the Interior Ministry, which runs the country's police, and said Afghanistan's criminal underworld could not operate without the support of the political "upperworld."

"The majority of police chiefs are involved," one senior police officer told the report's authors on condition of anonymity. "If you are not, you will be threatened to be killed and replaced."

Without naming officials, the report said it was possible that powerful interests in the Interior Ministry are appointing district police chiefs "to both protect and promote criminal interests."

The result is a "complex pyramid of protection and patronage, effectively providing state protection to criminal trafficking activities."

The spokesman for the counter-narcotics ministry said there is no evidence that high-ranking officials are involved in Afghanistan's drug trade.

"If there is evidence we welcome the evidence and the arrest will be on the spot," Zalmai Afzali said.

Poppy cultivation and the heroin it produces has become a major problem in Afghanistan, providing funds for the Taliban insurgency that has caused the deaths of more than 3,700 people this year.

Opium cultivation in Afghanistan rose 59 percent this year to 6,100 tons — enough to make 610 tons of heroin, nearly a third more than the world's drug users consume. The harvest provided more than 90 percent of the world's opium supply and was worth more than $3.1 billion.

Gen. Khodaidad, Afghanistan's deputy minister for counter-narcotics, told The Associated Press that next year's harvest will be as large as this year's in several key southern provinces where Taliban militants have a heavy presence. A U.S. official has also told the AP he expects next year's yield to be about the same.

The 210-page report, titled "Afghanistan's Drug Industry," is the first comprehensive assessment of the country's drug production, from poppy-growing farmers to international drug traffickers.

Barnett Rubin, director of studies and senior fellow at New York University's Center on International Cooperation, said his research has led to many of the same conclusions as the report's.

"There are many cases where honest prosecutors or police chiefs try to do something about corruption, and they say they receive phone calls from very high officials in Kabul saying to leave the people alone," said Rubin, an expert on Afghanistan.

Like the report, Rubin said he could not name names. "Getting indictable evidence is very, very difficult," he said. "I'm not mentioning any individual's name to you because I don't want to be sued or bumped off."

Interior Ministry spokesman Zemeri Bashary said the ministry has reformed its process for selecting police chiefs.

"At the moment we don't have any problems with our police chiefs," he said. "If the government is saying that poppy cultivation is prohibited, so they are obliged to implement the orders of the government."

Instead of sustained declines in cultivation, successful efforts to reduce poppy growing in one province often leads to increases elsewhere, the report found.

"History teaches us that it will take a generation to render Afghanistan opium-free," said Antonio Maria Costa, executive director of UNODC. "Those driving the drug industry must be brought to justice and officials who support it sacked."

Poppies take up less than 4 percent of the total cultivated area in Afghanistan, and most districts do not grow opium, the report said. But the $3.1 billion export value of last year's crop accounted for around one-third of total economic activity in the country, and about 13 percent of Afghans are involved in the trade.

The report says there is also a need to curtail demand. The major consumers of Afghanistan's opium are Iran, Pakistan, the United Kingdom, Italy, Spain and Germany, Buddenberg said.

Rubin said the report shows the international community's approach to the drug fight here is wrong.

"It should focus its efforts to remove big drug money from the political process," he said. "But instead what we have done is put big drug traffickers in positions of power, failed to take or support strong actions against them while we attack the livelihoods of small farmers and laborers through eradication, and they then turn to the Taliban or warlords for protection."