WASHINGTON—The U.S. military is secretly diverting aerial drones and weaponry from the Afghan battlefront to significantly expand the CIA's campaign against militants in their Pakistani havens.

The shift in strategic focus reflects the U.S. view that, with Pakistan's military unable or unwilling to do the job, more U.S. force against terrorist sanctuaries in Pakistan is now needed to turn around the struggling Afghan war effort across the border.

In recent months, the military has loaned Predator and Reaper drones to the Central Intelligence Agency to give the agency more firepower to target and bombard militants on the Afghan border.

The additional drones helped the CIA escalate the number of strikes in Pakistan in September. The agency averaged five strikes a week in September, up from an average of two to three per week. The Pentagon and CIA have ramped up their purchases of drones, but they aren't being built fast enough to meet the rapid rise in demand.

The escalated campaign in September was aimed, in part, at disrupting a suspected terrorist plot to strike in Western Europe. U.S. officials said Friday their working assumption is that Osama bin Laden and other senior al Qaeda operatives are part of the suspected terror plot—or plots—believed to target the U.K., France or Germany. They said they are still working to understand the contours of the scheme.