Another intelligence official said the target was a building in which a group led by Jalaluddin Haqqani, an Afghan Taliban commander whose men have previously conducted cross-border attacks on US-led troops in Afghanistan.
US drone attacks have intensified along the Afghan-Pakistan border in recent months, killing dozens of al-Qaeda-linked and Taliban leaders and fighters.
A similar attack killed Baitullah Mehsud, the chief of the Pakistani Taliban, in early August.
Earlier this month, Najmiddin Jalolov, a leader of an Uzbek armed group that is closely associated with al-Qaeda, died in a missile attack, also near Mir Ali.
Pakistan has officially condemned US drone attacks, saying they violate the country's sovereignty.