(Associated Press)

Pakistan-based insurgents planned and conducted some of the major attacks in Afghanistan recently, including the one on the U.S. Embassy in Kabul last week, with the support of Pakistan’s intelligence service, senior U.S. defense officials told Congress on Thursday.

“The Haqqani network ... acts as a veritable arm of Pakistan’s Inter-Services Intelligence agency,” Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, said. “With ISI support, Haqqani operatives plan and conducted” a truck bomb attack that wounded more than 70 U.S. and NATO troops on Sept. 11, “as well as the assault on our embassy” two days later.

“We also have credible intelligence that they were behind the June 28th attack on the Intercontinental Hotel in Kabul and a host of smaller but effective operations,” he added.

Mullen’s statement to the Senate Armed Services Committee, together with remarks by Defense Secretary Leon Panetta to the panel, were the most specific in a week of strong administration criticism of Pakistan.

“In choosing to use violent extremism as an instrument of policy,” Mullen said in a prepared opening statement, “the government of Pakistan, and most especially the Pakistani army and ISI, jeopardizes not only the prospect of our strategic partnership but Pakistan’s opportunity to be a respected nation with legitimate regional influence.

“They may believe that by using these proxies, they are hedging their bets or redressing what they feel is an imbalance in regional power,” he said. “But in reality, they have already lost that bet. ... They have undermined their international credibility and threatened their economic well-being.”

Both Mullen and Panetta resisted lawmakers’ attempts to describe what Sen. Carl Levin (D-Mich.), the chairman of the committee, called “the kind of options available to us to stop” Pakistani support for the insurgents and the “actions the administration is prepared to take” to ensure it.

“We’ve made clear that we are going to do everything we have to do to defend our forces,” Panetta said. “I don’t think it would be helpful to describe what those options would look like and what operational steps we might or might not face.”

The administration has insisted that Pakistan sever its ties with the insurgents, in particular the Haqqani forces based in the tribal region of North Waziristan, and supply all available intelligence on the group. Although senior administration officials have said they would prefer to work together with Pakistan against the group, they have indicated they are prepared to consider an expansion of drone strikes in the region, as well as surgical ground strikes, according to senior administration officials.

“The first order now,” Panetta told lawmakers, “is to put as much pressure on Pakistan as we can to deal with this issue.”

Levin noted that similar public pressure has continued for several years, and asked whether “Pakistan’s leaders are aware of what options are open to us, so they’re not caught by any surprise.”

“I don’t think they would be surprised by the actions that we might or might not take,” Panetta said.