The US has warned that Afghanistan is at risk of becoming a failed state unless Nato countries support its path towards democracy.
US Secretary of State Condoleezza Rice said the country would "come back to haunt us" if abandoned by the West.
She said the state's strategic position meant it risked becoming a haven for militant groups.
Last week, a top Nato commander called for troop reinforcements in Afghanistan due to spiralling violence.
Referring to a US decision to leave the country after the withdrawal of the Soviet Union in 1989, Ms Rice said, "We all came to pay for that."
She explained that the US should learn its lessons from Afghanistan.
"If you allow that kind of vacuum, if you allow a failed state in that strategic location, you're going to pay for it."
Speaking in Canada, where the country's role as part of the Nato force is unpopular, she said, "We owe it to the people of Afghanistan to help them finish the job."
Last month, Nato commanders took over from US-led coalition forces but there has been a resurgence of Taleban attacks, above all in the south of the country.
Nato commanders have requested 2,500 reinforcements to bolster the current 18,500-strong force, but so far member countries have been unwilling to commit more troops.
Nato officials are to hold a "force generation conference" in Belgium on Wednesday to try to boost troop numbers.
Pakistan's President Pervez Musharraf has warned that the Taleban are now more of a threat to the region's security than Osama bin Laden's al-Qaeda network.
"The centre of gravity of terrorism has shifted from al-Qaeda to [the] Taleban," he told European parliamentarians in Brussels.
He said a reinvigorated Taleban was particularly dangerous as, unlike al-Qaeda, it had its roots in the Afghan people.