In congressional testimony, senior defence and state department aides said that two years after United States-led forces ousted the Taliban from power in Kabul, Afghanistan remained beset by strife and poverty.
But they argued that US efforts to remake the country, including a $1.2 billion grant by President George Bush, were forging a new future for Afghans, after an agonised generation of war, occupation and tyranny.
"We anticipate that the challenge from the enemy will continue, they may attempt a fall offensive of some kind," said Peter Rodman, assistant secretary of defence for international security affairs.
"But the coalition and the Afghan government are ready. The enemy will certainly test us, but we expect that this offensive will fail. At that point, the enemy - not we - will face hard strategic decisions."
Rodman's comments to the House of Representatives International Relations Committee came hours after US-led coalition warplanes pounded Taliban fighters battling pro-Kabul forces in central Afghanistan.
"We anticipate that the challenge from the enemy will continue, they may attempt a fall offensive of some kind"
assistant secretary of defence for international security affairs
He defined the "enemy" as members of the Taliban, al-Qaida and "spoilers" like warlord Gulbuddin Hekmatyar.
Rodman noted that in recent weeks the Taliban had stepped up military activity, launching operations with sometimes as many as 100 fighters, in contrast to earlier attacks with smaller units.
But he said the only result of the new tactics was heavier casualties inflicted on the Taliban by US and Afghan government forces.
At the same hearing, state department coordinator for Afghanistan William Taylor admitted to disquiet at a deteriorating security situation along the Afghan-Pakistan border.
"It is particularly worrisome that Taliban units appear larger and better organised," he said, adding that the growing threat had prompted some humanitarian organisations to curtail operations.
But both men insisted that the Taliban resurgence, and other security threats, such as fighting between rival pro-government factions in the city of Mazar-i-Sharif last week, would not stunt the growth of a new Afghanistan.