Ryan Crocker also called on Islamabad to crack down on what he called Haqqani safe havens in Pakistan, reiterating a long-standing demand that has strained ties between the strategic allies.
"There is no question in our mind that the Haqqanis were responsible for these attacks," he told reporters.
"We know where their leadership lives and we know where these plans are made. They're not made in Afghanistan. They're made in Miranshah which is in North Waziristan, which is in Pakistan."
The Afghan Taliban claimed responsibility for the attacks on foreign embassies and parliament, which lasted 18 hours, killing 11 Afghan security forces and four civilians. Thirty-five insurgents died.
Though the death toll was relatively low considering the scale of the assault, it highlighted the ability of militants to strike high-profile targets in the heart of the capital even after more than 10 years of war.
The United States has repeatedly urged Pakistan's military to launch a major offensive in North Waziristan to go after the Haqqanis. Pakistan says it is already stretched fighting homegrown Taliban militants elsewhere near the Afghan border.
Pakistan, recipient of billions of dollars in US aid, sees the Haqqanis as a counterweight to the growing influence of rival India in Afghanistan, analysts say.
Pakistan denies that claim.
"Thousands of Pakistanis have died in terrorist actions inside Pakistan from individuals and groups that are in these so-called safe haven areas," said Crocker.
"So they really need to take action and that is going to be a major part of our dialogue going forward. That's what we are pressing them to do."
The US assertion that the Haqqanis were behind the recent attacks on Kabul and elsewhere, and renewed pressure for Pakistani action against the group, could deepen strains in the strategic alliance between Washington and Islamabad.
Ties have suffered since US special forces killed al Qaeda leader Osama bin Laden in a unilateral raid on Pakistan soil in May last year.
A November 26 NATO cross-border air attack which killed 24 Pakistani soldiers plunged relations to a low point.
The Haqqani network says it is no longer based in Pakistan and operates only from Afghanistan because it made serious battlefield gains.
Because it has the most seasoned fighters, and commanders who gained vast experience fighting Soviet occupation troops in Afghanistan in the 1980s, the Haqqanis are the most lethal insurgents.
Their effectiveness means they could also be spoilers in the Afghan reconciliation process.
COMMENTS (6)
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@Afghan Karachiite:
He said there was currently no proof..........big difference from your comment.
Pakistani establishment should realize that these Haqqani Network is terror network out to destroy not only the world peace but Pakistan also!
Yeah what else/..
US Chairman Joint Chiefs of Staff declared that attacks were not planned at Pakistani soil and.....Now, this gentleman says the other way round. Kia yeh khula tazad nahi?
Americans, you are simply pathetic!
It would appear that the USA isn't going to pull any punches when it comes to who's responsible for terrorism - even if it points a finger towards Pakistan. It would appear that the USA is still more concerned about protecting it's troops and allies than it's relationship with Pakistan --- something that Pakistan leadership hasn't quite figured out.