Den amerikanske ambassadøren i Islamabad sier det er nære forbindelser mellom Haqqani-nettverket og Pakistan, og at det er totalt uakseptabelt.
Konflikten mellom USA og Pakistan tilspisses enda mer.
USA har sagt det er Haqqani-nettverket som sto bak angrepet på Kabul denne uken.
Forsvarsminister Leon Panetta sa onsdag at USA ikke vil finne seg i at de ansvarlige går straffrie.
«Time and again we’ve urged the Pakistanis to exercise their influence over these kinds of attacks from the Haqqanis and we’ve made very little progress in that area,» Mr Panetta said Wednesday, a day after the Kabul siege.
«I’m not going to talk about how we’re going to respond. I’ll just let you know that we’re not going to allow these kinds of attacks to go on,» he said.
Pakistan’s foreign ministry condemned those remarks as «out of line», saying that «terrorism and militancy is a complex issue».
Ambassadør Cameron Munter fulgte opp lørdag. I et intervju med en pakistansk radiostasjon sa han at USA ikke kommer til å la angrepet på Kabul passere.
Det er det samme som å utfordre Pakistans regjering. USA sier Pakistan backer Haqqani, men at det ikke vil avskrekke USA.
Hvem blunker først?
The US ambassador to Pakistan, Cameron Munter, claims there are links between the Pakistani government and high-profile terrorist group the Haqqani network.
In blunt comments broadcast by state-run Radio Pakistan, Mr Munter said: «Let me tell you that the attack that took place in Kabul a few days ago that was the work of the Haqqani network,» he said, referring to a deadly miltant attack in on Tuesday.
«There is evidence linking the Haqqani network to the Pakistan government. This is something that must stop.
«We have to make sure that we work together to fight terrorism.»
Asked to provide evidence of the link with the Pakistani government, Mr Munter said only «we believe that to be the case».
The Haqqani network, which is closely allied to the Taliban, has been blamed for several high-profile attacks against Western, Indian and government targets in Afghanistan.
There is evidence linking the Haqqani network to the Pakistan government. This is something that must stop.
US ambassador Cameron Munter
The group is believed to be based in Pakistan but Islamabad has consistently denied links with militant groups.
The US has long urged Pakistan to take action against the Haqqani network and suspected the group had support within the Islamabad administration.