Ayman al-Zawahiri, who headed al-Qaeda and helped plot the 9/11 terrorist attacks, has been killed in a drone strike in Afghanistan, United States (US) President Joe Biden confirmed Monday.
He was slain in a CIA counter-terrorism operation in the Afghan capital of Kabul on Sunday.
Biden said Zawahiri had "carved a trail of murder and violence against American citizens," adding that "justice has been delivered and this terrorist leader is no more."
Zawahiri helped mastermind the devastating September 11 attacks with Saudi-national Osama Bin Laden. He took over the leadership of the international terrorist group al-Qaeda following the killing of Bin Laden in 2011.
Biden said he had green-lit the "precision strike" on the 71-year-old al-Qaeda leader, who officials say was on the balcony of a safe house when the drone fired two missiles at him.
The US president said Zawahiri's killing would help bring closure to families of the nearly 3,000 victims of the 2001 attacks in New York.
"No matter how long it takes, no matter where you hide, if you are a threat to our people, the United States will find you and take you out," said Biden.
"We shall never waver from defending our nation and its people," he continued.
According to US officials, no other people were killed or harmed in the drone strike, although other members of Zawahiri's family were present at the property.
A spokesman for the Taliban said the US military operation had violated international norms.
"Such actions are a repetition of the failed experiences of the past 20 years and are against the interests of the United States of America, Afghanistan and the region," the spokesman said, without mentioning Zawahiri.
US officials said their operation was within the law.
Zawahiri, an Egyptian-born eye doctor and theologian, led al-Qaeda for more than a decade from June 2011 until his death on Sunday.
Some experts have said he was the "operational brains" behind the September 11 attacks, which sparked the US war on terror in Iraq and Afghanistan.
According to Biden, Zawahiri helped plot multiple 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.
Following September 11, the US State Department offered a $25 million reward for information leading to Zawahiri's capture and slapped him with worldwide sanctions.
Under a 2020 agreement with Washington, the Taliban pledged not to host al-Qaeda or any other extremist group in areas of Afghanistan they control.
However, US officials claimed the Taliban knew of Zawahiri's presence in Kabul, with the Taliban and al-Qaeda years-long allies.
The targetting of Zawahiri comes nearly a year after the US's chaotic withdrawal from Afghanistan, which concluded its two-decade military presence there.
During the war in Afghanistan, some 176,000 people were killed, including 46,000 civilians, according to the Costs of War Project.