Washington, Feb 21 : Pakistan is providing its air base to the US to launch strikes against militants hiding in tribal areas, but has imposed restrictions on exactly which terrorist can be hit.

Taliban leader Mullah Omar and other big terrorists are never targeted due to their secret ties to Pakistani intelligence agencies, according to Christine Fair of Rand Corporation.

"These fellows are completely off-limits, and yet these fellows are so responsible for so much of the violence that is happening in Afghanistan," CBS News quoted her, as saying.

In an attempt to stop cross-border raids into Afghanistan, the CIA has launched more than 30 missile strikes since August, killing nine senior al Qaeda operatives.

But Fair argues that the strikes have also damaged America''s standing in Pakistan.

"It cannot be overstated how much anti-Americanism exists there, and it''s ironic, because we''ve spent, what, 12 billion dollars, and what we''ve gotten for that is a more insecure Pakistan that is more fearful of us than al Qaeda," Fair said.

For all of their drawbacks, US officials insist that without the drone attacks, the war in Afghanistan would be going even worse and the chances of another terrorist strike against the United States even greater. (ANI)