While not yet willing to blame the Haqqani network for assassinating former Afghan president, US military leaders say they will continue to strongly pressure Islamabad to prevent insurgents in Pakistan from commiting terror attacks in Afghanistan and then retreating into a "safe haven".
"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," defence secretary Leon E Panetta said during a Pentagon news briefing with Admiral Mike Mullen, chairman of the joint chiefs of staff.
"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," he said.
"That is not tolerable, and we have urged them to take steps."
Panetta declined to discuss specific strategies, including whether the US would consider unilateral action. He did say, however, "We are going to take whatever steps are necessary to protect our forces."
It's in the best interest of the Pakistanis to deal with terrorists within their borders, he said.
"Frankly, terrorism is as much a threat for them as it is for us," he said.
"And we keep telling them you can't choose among terrorists. 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."
Mullen said he made clear during his meeting last week with Pakistani Army Chief of Staff Gen. Ashfaq Parvez Kayani that Pakistan needs to do more.
Among issues he raised were the Haqqanis' proxy ties to Pakistan's Inter-Service Intelligence (ISI) agency and their role in killing coalition troops and Afghans in Afghanistan.
Based on current information, Mullen said he cannot confirm that the Haqqanis were behind the death of Burhanuddin Rabbani, former Afghan president heading reconciliation talks with the Taliban.