Donald Rumsfeld has said for the first time that the US military is working with anti-Taliban forces on the ground in Afghanistan.
The US Defence Secretary says there is good coordination with the ground, especially in the north of the country.
Officials say special force troops are providing food, ammunition and money to anti-Taliban forces.
"There is good coordination from the air with the ground in some places, particularly in the north," Mr Rumsfeld told reporters travelling with him to Whiteman Air Force Base in Missouri. "There is not that kind of coordination as of yet in the south."
A US official said separately that US special forces are supporting intelligence efforts to undermine the Taliban in southern Afghanistan. He said military action could increase markedly in coming days.
Mr Rumsfeld would not confirm reports that special operations forces were in Afghanistan.
"Any ground forces are in harm's way," he told reporters on the way to talk meet B-2 bomber crews at the Missouri Air Force base.
Gaining the support of anti-Taliban fighters across Afghanistan would help the US meet its goal of rooting out al-Qaida and toppling the Taliban, he said.
"It is going to be a lot easier, in my view, to try to persuade a number of them to oppose the Taliban and oppose al-Qaida and to help defeat them, than it is, in fact, to defeat (the terrorists)," he said.
At the Pentagon, Rear Admiral John Stufflebeem, deputy director of operations for the Joint Chiefs of Staff, told a news conference he would not comment on any aspect of ground operations.
"If or when they are on the ground, being there would make them the most vulnerable individuals engaged in this campaign," he said.
PA