The Haqqani militant network is a "veritable arm" of Pakistan's powerful intelligence service ISI, which supported the group as it launched a startling attack last week on the U.S. Embassy in Kabul, the top U.S. military officer said on Thursday, accusing Pakistan of "exporting" violent extremism to Afghanistan.

"The Haqqani Network ... acts as a veritable arm of Pakistan's Inter-Services Intelligence Agency," Admiral Mike Mullen, who steps down this month as chairman of the U.S. Joint Chiefs of Staff, told a U.S. Senate panel.

"With ISI support, Haqqani operatives planned and conducted (a Sept. 11) truck bomb attack, as well as the assault on our embassy. We also have credible intelligence that they were behind the June 28 attack against the Inter-Continental Hotel in Kabul and a host of other smaller but effective operations."

Mullen told US senators that "in choosing to use violent extremism as an instrument of policy, the government of Pakistan -- and most especially the Pakistani Army and ISI (intelligence service) -- jeopardizes not only the prospect of our strategic partnership, but also Pakistan's opportunity to be a respected nation with legitimate regional influence."