The U.S. options for potential retaliatory action rely mainly on air and missile strikes, but could also employ small teams of U.S. Special Operations troops already positioned along the border with Afghanistan. One of the senior military officials said plans for military strikes in Pakistan have been revised significantly over the past several years, moving away from a “large, punitive response” to more measured plans meant to deliver retaliatory blows against specific militant groups.

The official added that there is a broad consensus in the U.S. military that airstrikes would at best erode the threat posed by al-Qaeda and its affiliates, and risk an irreparable rupture in the U.S. relationship with Pakistan.

“The general feeling is that we need to be circumspect in how we respond so we don’t destroy the relationships we’ve built” with the Pakistani military, the second official said.