U.S. President Joe Biden has announced that al-Qaeda leader Ayman al-Zawahiri was killed in a drone strike in Kabul, Afghanistan. Zawahiri was regarded as one of the world's most wanted terrorists and had helped coordinate the September 11 attacks in 2001. He became head of al-Qaeda in 2011 after its leader Osama bin Laden was killed by U.S. forces in Pakistan during a raid.