The White house has blocked a secret plan into the tribal regions of Pakistan to capture or kill Osama bin Laden and his top lieutenants.

The Pentagon had drafted a secret plan to put American commandos in Pakistan's tribal areas, along the Afghanistan border, to hunt for Bin Laden and his top aides who took refuge there. But the White House has balked at giving the mission a green light, The New York Times reported late Monday.

Although the Special Forces attack plan was devised six months ago, infighting among US intelligence agencies and among White House offices have blocked it from being implemented, it added.

The Times noted there were "mounting frustration" in the US Defense Department about the continuing delay in implementing the plan.

US Intelligence reports have concluded that bin Laden has re-established a network of new training camps, and the number of recruits in those camps has risen to as many as 2,000 in recent months from 200 earlier this year.

For now at least, the United States is only conducting air strikes in the area, based on intelligence reports or when in 'hot pursuit' of militant units.

In particular, the paper says there is concern about the impact on Pakistan's government, a key US ally, if the presence of US ground troops became public.

But some political analysts believe that the US is protecting Qaeda's leader to seek a justification for the so-called war on terror.