Providing developmental support to poor farmers is the key weapon against Afghanistan's opium menace, not military force to destroy poppy crops, the World Bank and the Department of International Development of Britain said Tuesday in a joint report.

Experts on Afghanistan's massive opium output — a major source of crime, corruption and funds for armed groups — gathered in Tokyo as a two-day global conference on the country's rehabilitation started Tuesday.

Afghanistan allegedly accounts for over 90 percent of the world's illicit opium.

"Eradication (of poppy fields) looks superficially attractive," but it is not a sustainable solution both economically or politically, William Byrd, an adviser to the World Bank and an expert on opium issues, told reporters at the Foreign Correspondents' Club of Japan in Tokyo.

Poor farmers grow opium poppies to survive. Without alternative sources of revenue, security or good governance in Afghanistan, there will be no end to the opium problem, Byrd warned.

The joint report stresses measures to develop rural areas, including building irrigation systems to grow alternative crops, increasing domestic livestock and urging international bodies and firms to increase local procurement and employment.

The report says the opium trade is equivalent to around 30 percent of Afghanistan's licit gross domestic product, and millions of Afghans benefit from it either directly or indirectly.

"The opium economy lies at the heart of the challenges Afghanistan faces," Byrd said. "There is no shortcuts, no silver bullets, no easy way or one-dimensional solution to eliminate the opium problem in Afghanistan."