A crackdown by Pakistan's military on these sanctuaries would have greater impact than any other option available to top American commanders in Afghanistan, 'Washington Post' reported quoting top US officials.

But, the paper said, a move by Islamabad against these groups is considered unlikely at least by US Administration's timetable as the Pakistan Government long standing connections to the Haqqani network and the Taliban.

The Post said that Washington has sought to compensate this by ramping up raids by special forces and military air patrols on the Afghan side of the border and by sharply increasing CIA drone strikes in Pakistan.

Over the past two months, the US spy agency has nearly doubled drone strikes in an intense campaign aimed at crippling the Taliban, to put meaningful pressure on its leaders to seek peace.

"Escalated air strikes and special operation raids have disrupted the Taliban movements and damaged local cells. But officials said that the insurgents have absorbed these blows by moving their cadre", the Post said.

General David Petraeus, the top US commander in Afghanistan has touted the success of recent operations and indicated that the military thinks that it will be able to show meaningful results by December, when President Barack Obama is to undertake a strategic review of the war in Afghanistan.

'Washington Post' said that US commanders acknowledged that major obstacles remain as American drones are not being allowed by Islamabad to patrol the restive city of Quetta, the capital of Pakistan's Balochistan province where top Taliban leaders including their chief Mullah Omar is believed to be holed up.