Leader of al Qaeda has potentially serious 'heart complaint': report

News of Zawahiri's ailing health follows reports Wednesday indicating that Hamza bin Laden, the son of former al Qaeda leader Osama bin Laden who himself had been tapped to lead the group in the future, had been killed.

Three U.S. officials confirmed to NBC News that the U.S. believes the younger bin Laden is dead but would not give any further information Wednesday.

Osama bin Laden, leader of the terror group during the 2000s and in particular for the 9/11 attacks, was killed in 2011 by a Navy SEAL raid.