A senior US general has warned President Barack Obama's deadline to begin pulling troops out of Afghanistan is encouraging the Taliban.
US General James Conway, head of the US Marine Corps, said the deadline was "giving our enemy sustenance".
Gen Conway warned that US forces in southern Afghanistan will likely have to stay in place for several years.
His comments are likely to fuel debate over US strategy in Afghanistan and Mr Obama's July 2011 withdrawal date.
US administration officials say privately they are not surprised to hear the comments from the general, who, correspondents say, has typical US Marine Corps bluntness - and is also about to retire.
Gen Conway, who just returned from Afghanistan, said he is concerned the date may signal to the Taliban that the US was preparing to wind down the war.
"In some ways we think right now it's probably giving our enemy sustenance. We think that he may be saying to himself, in fact we've intercepted communications that say, 'Hey, we only have to hold out for so long,'" Gen Conway told a Pentagon news conference.
"I honestly think it will be a few years before conditions on the ground are such that turnover will be possible for us," he said of Marines in the southern provinces of Helmand and Kandahar.
The BBC's Nick Childs says the statements made by the general highlight the manner in which American political and military leaders continue to differ about how fast security can be handed over to the Afghan authorities.
General Conway said that Afghan units "somewhere" may be able to take the lead in security, but not in the south, which the general called the "birthplace" of the Taliban insurgency.
The White House said on Tuesday the president planned to review the Afghan war in December.
"So we're still on the path that the president laid out," said deputy national security adviser John Brennan.
President Obama and his supporters defend the deadline as a way of pushing Afghan leaders to act quickly to take charge of their security.
But General Conway said Taliban foot soldiers would likely suffer a blow to morale after July 2011 passes with no dramatic departure of American forces, "and come the fall we're still there hammering them like we have been".
Foreign troops fighting the Taliban operate under US and Nato command and are supporting Kabul's Western-backed government against a Taliban-led insurgency that has gained strength in recent years.
Attacks from Islamist insurgents have increased on Nato-led forces in Helmand and Kandahar as troops have attempted to secure Taliban strongholds in the region.
The general told the news conference that 30,000 US troops arrived on the ground in Afghanistan earlier this month, putting the number of US troops close to 100,000.
He spoke a day after the US general incharge of training Afghan forces played down prospects for a major transfer of security duties for another year at least.
US Defence Secretary Robert Gates has suggested any troop reduction after mid-2011 would be modest.