Ambassador William Wood said preliminary data show that Afghan farmers harvested 457,135 acres of opium poppies this year, compared to 407,715 acres last year. The growing industry fuels the Taliban, crime, addiction and government corruption.
Government-led eradication efforts destroyed about 49,420 acres of poppies this year, a "disappointing" outcome, Wood told reporters at his private residence overlooking Kabul.
Wood said he strongly supports forced eradication, alluding to U.S.-led poppy-spraying in Colombia. But he said there is "not yet an international consensus" on the practice.
Drug cultivation "threatens security and governance and stability in Afghanistan" and kills Afghans and others, he said.
Afghan President Hamid Karzai last year rejected U.S. offers to spray this year's illicit crop, after Afghans said the herbicide could affect livestock, crops and water — fears the U.S. calls unfounded.
Afghanistan last year accounted for 92 percent of global opium production, up from 70 percent in 2000 and 52 percent a decade earlier. With the higher yields, global opium production increased 43 percent between 2005 and 2006.
Gen. Dan McNeill, the top general in charge of NATO-led troops here, has said he expects Western soldiers to step up anti-drug efforts, though they do not participate in eradicating poppy fields.
Taliban fighters are believed to tax and protect poppy farmers and drug runners, but so are Afghan government officials and pro-government tribes.
Afghan troops, meanwhile, clashed with suspected militants in eastern Afghanistan, near the Pakistani border, killing several suspected militants, a Defense Ministry statement said Tuesday. The region's rising violence comes as U.S. officials say al Qaeda is regrouping there.
The skirmish happened just across from Pakistan's lawless North Waziristan region, where recent attacks killed more than 70 people, mostly police and soldiers.
Pakistan's authorities were scrambling to salvage a peace agreement between the government and village elders. Pro-Taliban militants renounced that agreement after last week's storming of Islamabad's radical Red Mosque, where more than 100 people died after an eight-day siege ended with a commando attack on Islamist militants.
U.S. officials repeatedly said that the North Waziristan deal allowed militants to cross the border.