Panetta and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, spoke to reporters at a Pentagon briefing Tuesday, the same day former Afghan President Burhanuddin Rabbani, who had headed his country's peace council, was assassinated. Rabbani was in charge of negotiating with the Taliban.
While not directly blaming the violent Haqqani network, which has safe haven in Pakistan's tribal areas, for the assassination, Panetta and Mullen spoke of the need to keep pressure on Pakistan to check the insurgents, the Defense Department said on its Web site.
"Our biggest concern right now is to put as much pressure as possible on the Pakistanis to exercise control from their side of the border," Panetta said.
"We have continued to state that this cannot happen. We cannot have the Haqqanis coming across the border attacking our forces and [Afghans] and disappearing back into a safe haven. That is not tolerable, and we have urged them to take steps."
The secretary did not spell out specifics but said the United States will "take whatever steps are necessary to protect our forces" adding it is in the best interest of Pakistani to deal with terrorists within its borders."
"If you are against terrorism, you have to be against all forms of terrorism. And that is something we just have to continue to stress," he said.
Mullen said he made clear in his meeting last week with Pakistani Army Chief of Staff Gen. Ashfaq Parvez Kayani that Pakistan needs to do more. He said the Haqqanis' ties to Pakistan's Inter-Service Intelligence agency and their role in killing coalition troops and Afghans in Afghanistan was "the heart of the discussion," stressing such activities must stop.
"That is not a new message, but it is one that [Kayani] clearly understands," Mullen said. "And I think it is one we have to keep reiterating."
The Haqqanis also are suspected of being responsible for last week's attacks on the U.S. Embassy in Kabul.