Al-Qaeda leader Ayman al-Zawahiri has been killed in a CIA drone strike in Afghanistan's Kabul, United States President Joe Biden announced on Monday. The operation had been planted over many months.

Al-Zawahiri was killed on Sunday in the biggest blow to the group since its founder Osama bin Laden was killed in 2011.

“Justice has been delivered and this terrorist leader is no more,” Biden said in a special televised address from outside the White House, reports Aljazeera.

Intelligence had located al-Zawahiri’s family in Kabul earlier this year, Biden said, adding that no members of the family or civilians had been killed in the attack.

An Egyptian surgeon with a $25m reward on his head, al-Zawahiri helped coordinate the September 11, 2001 attacks on the US that killed nearly 3,000 people.

Earlier, US officials speaking on the condition of anonymity told reporters earlier that the CIA carried out a drone attack in the Afghan capital Kabul using two missiles.

Al-Zawahiri was on his balcony at the time, they said.

“It’s a significant blow,” Colin Clarke, research director at the Soufan Group, a global security firm, told Al Jazeera, adding that his presence in Kabul was also interesting in what it suggested about his relationship with the Taliban.

“It tells us he’s gotten far more comfortable over the past years since the Taliban took over,” Clarke said.

The Taliban confirmed the attack in Kabul, and condemned it as a “violation of international principles”.

In a statement, US Secretary of State Antony Blinken said that al-Zawahiri’s presence in Kabul “grossly violated the Doha Agreement and repeated assurances to the world that they would not allow Afghan territory to be used by terrorists to threaten the security of other countries”.

Washington and the Taliban signed the deal in 2020 paving the way for the withdrawal of US-led foreign forces in return for a guarantee from the Taliban not to allow groups such as al-Qaeda and ISIL (ISIS) to operate on Afghan soil. The US forces withdrew just before an August 31 deadline in what turned out to be a chaotic exercise.

Blinken said that by allowing al Qaeda shelter in Afghanistan, the Taliban had also “betrayed” the Afghan people and “their own stated desire for recognition from and normalization with the international community”.