The US has killed the leader of al-Qaeda, Ayman al-Zawahiri, in a drone strike in Afghanistan, President Joe Biden has confirmed.

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

Mr Biden said Zawahiri had "carved a trail of murder and violence against American citizens".

"Now justice has been delivered and this terrorist leader is no more," he added.

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 he was one of the US's "most wanted terrorists".

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

Other family members were present, but they were unharmed and only Zawahiri was killed in the attack, they added.

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

His killing will bring closure to families of the nearly 3,000 victims of the 2001 attacks, Mr Biden added.

"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".

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.

A Taliban spokesman described the US operation as a clear violation of international principles - but did not mention Zawahiri.

"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.

However, US officials maintained that the operation had a legal basis.

The killing of Zawahiri comes nearly a year after US troops completed their withdrawal from Afghanistan on the orders of Mr Biden, bringing an end to a 20-year military presence there.

Under a 2020 peace deal with the US, the Taliban agreed not to allow al-Qaeda or any other extremist group to operate in areas under their control.

However, the Taliban and al-Qaeda are long-time allies and US officials said the Taliban were aware of Zawahiri's presence in Kabul.

US Secretary of State Antony Blinken said that by hosting and sheltering Zawahiri in Kabul, the Taliban had "grossly violated" the peace agreement.

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 was believed by some experts to have been the "operational brains" behind the 11 September 2001 attacks.

The drone strike is the first known US strike inside Afghanistan since the military pullout last August.

Days before the withdrawal, a miscalculated US drone strike killed 10 innocent people in Kabul, including an aid worker and seven children. The US said it was a "tragic mistake" and had been aiming to target a local branch of the Islamic State group.