Afghanistan's Northern Alliance says it believes Osama bin Laden and Taliban leader Mullah Mohammad Omar are in or near the southern city of Kandahar, where US marines landed this morning.
Northern Alliance Foreign Minister Mr Abdullah Abdullah also said he would send commanders but no troops to fight Taliban forces in the city.
"I think Osama and his forces are contained, they are not free to operate throughout the country. This might have been the factor that made them [the US soldiers] move," he said. "It's my information that [Mullah Omar and bin Laden] are both together," he said.
The arrival of significant numbers of US troops in an area not controlled by the anti-Taliban Northern Alliance marks a new phase in the US military campaign in Afghanistan.
It comes just a day before non-Taliban groups are due to meet in Bonn for talks on setting up a broad-based government in Afghanistan, which has had 20 years of war.
"[The US deployment] is part of the campaign against terror. I am of course not aware of the details of what is happening there," Mr Abdullah told a news conference.
He said the Bonn talks were important but played down the chance of much concrete progress.
"Expectations should not be too high. We are in transition from war to peace, a war which lasted 23 years," he said. "It cannot be done in two or three days".