The White House has confirmed al-Qaeda's second-in-command Abu Yahya al-Libi has been was killed, calling it a "major blow" to the terror network.
A U.S. official said he was killed in a U.S. drone strike. Officials say al-Libi was the target of the latest strike in the North Waziristan region Monday.
Pakistani officials say at least 15 people were killed in the airstrike, one of several in recent days that have killed at least 27.
Al-Libi is best known for escaping a high security U.S. prison in Bagram, Afghanistan, in 2005.
Pakistan's Foreign Ministry summoned Deputy U.S. Ambassador Richard Hoagland, instructing him to convey "serious concern regarding drone strikes in Pakistani territory."
The Foreign Ministry called the drone strikes "unlawful, against international law and a violation of Pakistani sovereignty."
Al-Libi rose to al Qaeda's second in command shortly after Osama bin Laden's assassination on May 2, 2011.