WASHINGTON (AFP) - NATO has failed to stem the vast opium trade in Afghanistan that helps finance Taliban insurgents despite an eight-year effort, the top US military officer said on Thursday. Countering narcotics networks is crucial to weakening the Taliban and allied insurgent groups, Admiral Mike Mullen, chairman of the US Joint Chiefs of Staff, told a Senate hearing.Strategically my view is it has to be eliminated, Mullen said. We have had almost no success in the last seven or eight years doing that, including this years efforts, he said. Afghanistan produces 90 per cent of the worlds opium, the raw material for heroin across Europe, Central Asia and the Middle East while cash from the trade helps insurgents buy weapons, according to officials. The Taliban, ousted from power seven years ago by a US-led coalition, has been reaping close to 100 million dollars a year from the opium trade. A key element in tackling the problem was to offer Afghan farmers alternatives to the opium crop, the admiral said. Weve got to have a concerted effort, not only the US, the international community, to displace it (opium crop) and to do it in a way that makes sense, Mullen said. Officials in President Barack Obamas administration say they want to emphasize alternative crops and avoid aggressive eradication operations that could alienate Afghans. Mullen said NATO-led forces have stepped up operations against drug networks after the alliance last year eased rules for targeting narcotics rings. Recent rules of engagement have allowed us to go after labs, people associated with labs, he told the Senate Foreign Relations Committee. Thats a step in the right direction but until we are able to execute a comprehensive agricultural strategy, its going to be very difficult to really have a strategic impact on that. The bulk of Afghanistans opium production is based in the south of the country, which is also the heart of the Taliban-led insurgency. Obama has ordered more than 21,000 additional US troops to Afghanistan, with most of the extra troops deploying to the south.