President Joe Biden confirmed that the US killed al-Qaeda leader Ayman al-Zawahiri in an Afghanistan drone strike.
On Sunday, he was killed in a CIA counter-terrorism operation in Kabul, Afghanistan's capital.
He and Osama Bin Laden worked together to plan the 9/11 attacks, and he was one of America's "most wanted terrorists."
According to Mr. Biden, Zawahiri has "carved a trail of murder and violence against American citizens."
"Zawahiri has been a leader of al-Qaeda since the United States delivered justice to bin Laden 11 years ago," Biden said. "From hiding, he coordinated al-branches Qaeda's and operations all over the world, including setting priorities for operational guidance and calling for and inspiring attacks against US targets."
"Justice has been served, and this terrorist leader is no longer alive," he added.
After Bin Laden's death in 2011, Zawahiri took over al-Qaeda.
According to officials, Zawahiri was on the balcony of a safe house when the drone launched two missiles at him.
Other family members were present, but they were unharmed, and they added that only Zawahiri was killed in the attack.
Mr Biden said Zawahiri had also masterminded other acts of violence, including the suicide bombing of the USS Cole naval destroyer in Aden in October 2000 which killed 17 US sailors, and the 1998 attacks on the US embassies in Kenya and Tanzania, in which 223 people died.
He insisted that Afghanistan would never again become a safe haven for terrorists.
After months of planning, Mr Biden said he had given final approval for the "precision strike" on the 71-year-old Egyptian.
Mr. Biden added that his death will bring closure to the families of the nearly 3,000 victims of the 2001 attacks.
"Regardless of how long it takes or where you hide, if you are a threat to our people, the United States will find you and take you out," Mr Biden said, adding that "we shall never waver from defending our nation and its people."
Mr. Biden claimed that Zawahiri was also responsible for other acts of violence, such as the suicide bombing of the USS Cole naval destroyer in Aden in October 2000, which killed 17 US sailors, and the 1998 attacks on US embassies in Kenya and Tanzania, which resulted in the deaths of 223 people
He vowed that Afghanistan would never again be a haven for terrorists.
The US operation, according to a Taliban spokesman, is a clear violation of international principles, but Zawahiri was not mentioned.
"Such actions are a reenactment of failed experiences over the last two decades and are detrimental to the interests of the United States of America, Afghanistan, and the region," the spokesman added.
However, US officials insisted that the operation was legal.
The assassination of Zawahiri comes nearly a year after US troops completed their withdrawal from Afghanistan on Mr Biden's orders, ending a 20-year military presence there.