Secretary of State Condoleezza Rice acknowledged on Sunday that the United States was surprised by the strength of Afghanistan's Taliban militia five years after its ouster from power in the wake of the September 11 attacks on New York and Washington.
But Rice told Fox News Sunday that Nato forces were inflicting heavy losses on the Taliban and that the rebels posed no "strategic threat" to the embattled government of President Hamid Karzai.
In one of a series of interviews on the eve of the fifth anniversary of the September 11 al Qaeda attacks, Rice said it had been expected that the Taliban would attempt to regain power after being ousted by US-led forces in late 2001 for providing a safe haven to al Qaeda leaders.
"Of course they're going to fight back, even if they're on the ropes, they're going to fight back," she said.
But she went on to admit that "they came back somewhat more organised and somewhat more capable than would have expected," she said.
Rice was speaking two days after the top British commander in Afghanistan, Brigadier Ed Butler, said the fighting between Nato forces and the Taliban in recent weeks had been "extraordinarily intense".
"The intensity and ferocity of the fighting is far greater than in Iraq on a daily basis," he said.
But Rice said the Nato forces were making significant progress against the Taliban since they replaced US-led troops in the volatile south of the country six weeks ago.
"They're learning a very brutal lesson as they encounter Nato forces that are destroying them in very large numbers," she said.
"The Taliban is taking a beating in this.
"The notion that somehow this is a strategic threat to the Karzai government, I think this is not the case."
The Nato-led force took over military command of southern Afghanistan on July 31 from the US-led coalition that toppled the fundamentalist Taliban government in late 2001.
The force - which has around 10,000 mainly British, Canadian and Dutch troops in the south - has come under regular attack, particularly in Helmand and Kandahar provinces.
At the same time attacks against government and US coalition forces elsewhere in the country have continued.
On Sunday, a respected provincial governor in eastern Afghanistan was killed along with his nephew and bodyguard by a suicide bomber.
And on Friday a suicide bombing in Kabul killed 16 people, including two US soldiers.