Washington: US has said it will put "as much pressure as possible" on Pakistan to exercise control on insurgent groups from "their side of the border",  even as top Pentagon officials reiterated that America has made progress in weakening the Taliban and al-Qaeda.

"We are going to take whatever steps are necessary to protect our forces. I'm not going to talk about particular strategies to implement that commitment," Defence Secretary, Leon Panetta, told reporters at a joint Pentagon news conference with Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff.

"But 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. We've continued to state that this cannot happen. We cannot have the Haqqanis coming across the border, attacking our forces, attacking Afghanistanis and then disappearing back into a safe haven. That is not tolerable," Panetta said.

The Haqqani network is blamed for a recent bombing attack that injured 77 US troops at a base in Wardak province and for an elaborate assault on September 13 on the US embassy and NATO headquarters in Kabul.

The Defence Secretary's comments came shortly after a suicide bomber laden with explosives in his turban yesterday assassinated Afghanistan's former president Burhanuddin Rabbani, who was leading efforts to talk peace with insurgents.

Panetta said the US has made progress in weakening the Taliban and al-Qaeda.

"We have made progress in going after their leadership. But they now are resorting to these kinds of attacks, to these kinds of high-level assassinations, which, are of concern. We have to take steps to try to make sure that we protect against that.

"We are in the process of doing that. We're working with the Afghans to try to discuss with them steps on how we can provide better protection so that this does not occur. But the bottom line still remains that we are moving in the right direction. And we can't let some of these sporadic events deter us from the progress that we've made," he said.