The US has warned there must be no amnesty for Taliban leader Mullah Mohammed Omar.
Opposition fighters are said to be closing in round Kandahar where Omar has ordered his supporters to fight to the death.
But US Defence Secretary Mr Donald Rumsfeld says they would fiercely resist any deal that allowed Omar to go free.
The Pentagon says the situation in the area remains "fluid", with negotiations taking place between the opposition forces and the Taliban for the city's surrender.
"I can assure you that the United States would vigorously oppose any idea of providing him amnesty or safe passage of any type," he said.
He also made clear that the US was anxious to question a senior al-Qaida operative reportedly captured in Afghanistan by Northern Alliance forces.
Ahmed Abdel Rahman, 35, the son of a sheikh convicted for the 1993 bombing of the World Trade Centre, reportedly ran a terrorist camp in Afghanistan, according to US intelligence officials.
Meanwhile an Afghan warlord is preparing to attack a suspected mountain hideout of Osama bin Laden, it was reported this evening.
Hazrat Ali, the security chief for eastern Nangarhar province, says Tora Bora must be targeted by anti-Taliban forces soon.
The camp is in a high mountain valley filled with hidden caves near the Pakistani border.