The most senior US military officer has accused Pakistan's spy agency of supporting the Haqqani group in planning and conducting last week's attack on the US embassy in Kabul.
"The Haqqani network... acts as a veritable arm of Pakistan's Inter-Services Intelligence Agency," Adm Mike Mullen told a Senate panel.
In July he said Pakistan sanctioned the killing of journalist Saleem Shahzad.
Pakistan's government called that statement "irresponsible".
Pakistani officials have consistently denied links with militant groups.
'Credible intelligence'
At least 25 people died during the 20-hour attack on the US embassy, Nato headquarters and police buildings in Kabul on 22 September.
The dead included 11 civilians, among them children, along with at least four police and 10 insurgents.
"With ISI support, Haqqani operatives planned and conducted a truck bomb attack, as well as the assault on our embassy," said Adm Mullen, who steps down this month as chairman of the US Joint Chiefs of Staff.
"We also have credible intelligence that they were behind the 28 June attack against the Inter-Continental Hotel in Kabul and a host of other smaller but effective operations."
The Haqqani network, which is closely allied to the Taliban and reportedly based in Pakistan, has been blamed for several high-profile attacks against Western, Indian and government targets in Afghanistan.
It is often described by Pakistani officials as a predominantly Afghan group, but correspondents say its roots reach deep inside Pakistani territory, and speculation over its links to Pakistan's security establishment refuses to die down.