Small groups of US Special Forces are working inside Afghanistan, Defence Department sources have confirmed, amid hints that their role and numbers may soon be expanded substantially.
Leaflets are also being dropped and radio broadcasts are telling Taliban fighters that US soldiers will soon be among them and explaining how to go about surrendering to them.
"Attention! People of Afghanistan, United States forces will be moving through your area," the leaflets read, according to transcripts released by the Pentagon.
"We are here for Osama bin Laden, al-Qaeda and those who protect them! Please, for your own safety, stay off bridges and roadways, and do not interfere with our troops or military operations. If you do this, you will not be harmed."
Speaking to journalists last night the Secretary of Defence, Mr Don Rumsfeld, gave as clear a definition yet of the US forces' mission statement when he said their role in Afghanistan would be over "when the Taliban and al-Qaeda are gone".
But he and the Pentagon were not willing to confirm ground deployments, and spokesman Rear Admiral John Stufflebeem warned that "if or when" it happens such troops are the most vulnerable and that the Pentagon will not be detailing their role while still vulnerable.
Washington has told Pakistan, however, that its special forces will be conducting "hit-and-run" operations in Taliban-ruled areas to flush out Osama bin Laden, members of his al-Qaeda network and Taliban leaders, a Pakistan military official said in Islamabad.
And agencies report that the groups already being infiltrated are concentrating on the south of the country in an attempt to make contact with and woo Pashtun tribal leaders.
Both Pakistani and Northern Alliance sources are also confirming that American military advisers are now in place liaising with the latter's commanders in the north of the country and on the front lines facing Kabul.
They are not involved in combat roles.
Military officials in Pakistan have said that in the past 48 hours there had been increased activity by American forces at Jacobobad, one of two Pakistani airbases designated by the Pakistani President, Gen Pervez Musharraf, as staging posts for what have been described as "search-and-rescue operations".
Defence Department officials have also been making clear their conviction that the war will not be won from the air and that the US will have to use the full spectrum of its assets.
After heavy bombing attacks overnight on the 13th day of bombing, heavy attacks were reported to be continuing in the Taliban's headquarters city of Kandahar as well as Kabul.
The Pentagon reported attacks on Thursday on 18 locations, or "engagement zones", by up to 90 aircraft of a wide range of types, 75 of them carrier-based.
Targets included airbases, troop deployments, dispersed armour, artillery emplacements and vehicle supply and maintenance depots.
Three more humanitarian flights of relief supplies delivered some 52,000 individual rations to bring the total to half a million to dropped date.
Admiral Stufflebeem said they were now also confident that they had "severed" Taliban communications, but that the battle for the strategically important city of Mazar-e-Sharif is continuing.
Mr Rumsfeld also later confirmed the US has supplied arms, food and money to opposition forces.
