The havens carved out by the Taliban and other insurgents in Pakistan have become the "most worrisome" part of the US-led war in Afghanistan, says US Defence Secretary Robert Gates.
Washington had a similar perch in Pakistan when US and Pakistani officials supported Afghanistan's mujahideen rebels against the Soviet Union in the 1980s - "and let me tell you, it made a big difference", he said Sunday.
"I think as long as they have a safe haven to operate there, it's going to be a problem for us in Afghanistan," he told NBC's "Meet the Press".
"I think it's the safe haven on the Pakistani side of the border, not just for Al Qaeda but for the Taliban, for the Hakani network, for Gulbaddin Hekmatyar and other affiliated groups that are all working together," Gates told MSNBC.
"They're separate groups, but they're all working together, and I think as long as they have a safe haven to operate there, it's going to be a problem for us," he added.
Meanwhile, Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, told CNN's "State of the Union" that Afghanistan President Hamid Karzai's inability to improve security and public services have contributed to "the situation that we're in right now" - where the Taliban and its allies, including Al Qaeda, are on the offensive.
With the war spilling over into Pakistan, where the Taliban have long had a foothold in the tribal areas along the mountainous border, the US is reported to be responsible for periodic airstrikes that target suspected militant leaders.
Neither Gates nor Mullen would discuss those strikes, which Pakistani officials say are mostly conducted by armed surveillance drones.
But Gates said Pakistan now believes the border area "is as big a risk to the stability of Pakistan as it is a problem for us in Afghanistan".
European, Pakistani and Afghan officials are taking part in the administration's strategy review, and the process could be done in "a few weeks", Gates said.