He was killed in a counter-terrorism operation carried out by the CIA in the Afghan capital, Kabul, on Sunday, BBC reported.

President Biden said Zawahiri had "carved a trail of murder and violence against American citizens" adding "Now justice has been delivered and this terrorist leader is no more".

Officials said Zawahiri was on the balcony of a safe house when the drone fired two missiles at him.

His other family members were also present in the house at the time of the strike, but they were unharmed and only Zawahiri was killed, they added.

Biden said he had given the final approval for the "precision strike" on the 71-year-old al-Qaeda leader.

Zawahiri took over al-Qaeda after the death of Osama bin Laden in 2011. He and Bin Laden plotted the 9/11 attacks together and had ever since become one of the US's "most wanted terrorists".

The killing of the al-Qaeda leader would bring closure to families of the victims of the 2001 attacks, President Biden said, adding that 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.

"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 Mr Biden, adding that "we shall never waver from defending our nation and its people".

A Taliban spokesman described the US operation as a clear violation of international principles.

"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 added.

Zawahiri, an eye surgeon who helped found the Egyptian Islamic Jihad militant group, took over the leadership of al-Qaeda following the killing by US forces of Bin Laden in May 2011.

Before that, Zawahiri was often referred to as Bin Laden's right-hand man and the chief ideologue of al-Qaeda.

He is believed by some experts to have been the "operational brains" behind the 11 September 2001 attacks in the United States.

(With UNI inputs)