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 year''s efforts," he said.

Afghanistan produces 90 percent of the world''s 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 (77 million euros) 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.

"We''ve got to have a concerted effort, not only the United States, the international community, to displace it (opium crop) and to do it in a way that makes sense," Mullen said.

Officials in President Barack Obama''s administration say they want to emphasize alternative crops and avoid aggressive eradication operations that could alienate Afghans.