US Defence Secretary Robert Gates on Sunday warned that the failure of the international force in Afghanistan would increase the security threat to Europe.
Gates also renewed criticism of some European allies, telling the annual Munich Conference on Security Policy that disputes within NATO over troops in Afghanistan risked turning it into a "two tier" alliance of some countries ready to fight and others refusing.
"Instability and conflict abroad have the potential to spread and strike directly at the hearts of our nations," he told the conference.
"But I am concerned that any people on this continent may not comprehend the magnitude of the direct threat to European security," he told the forum, where ministers and top officials from around the world also discussed Kosovo's looming independence and Russia's relations with the West.
"For the United States September 11 was a galvanizing event -- one that opened the American public's eyes to dangers from distant lands."
Afghanistan's Taliban militia, who had provided safe haven to Osama bin Laden's Al-Qaeda network, were ousted from power in 2001 by a US-led invasion after the suicide plane attacks on the United States.
But international forces and the Afghan army have been confronted by a renewed Taliban insurgency, notably in the south of the country where the international force has seen heavy fighting.
Gates warned that success for the Taliban would be a huge morale boost for Islamic extremism worldwide, and said a reticent European public should remember this.