In a televised address, U.S. President Joe Biden Biden said the strike in Kabul, Afghanistan had been carried out on Saturday. "I gave the final approval to go get him," he said, adding that there had been no civilian casualties.
"Justice has been delivered and this terrorist leader is no more," Biden said.
A senior administration official said Zawahiri had been killed on the balcony of a house in Kabul in a drone strike, and that there had been no US boots on the ground in Afghanistan.
The official said that Zawahiri's presence in the Afghan capital Kabul was a "clear violation" of a deal the Taliban had signed with the US in Doha in 2020 that paved the way for the US withdrawal from Afghanistan.
Before the president spoke, word of the al-Zawahiri strike came from administration sources remaining anonymous in order to convey information.
"Over the weekend, the United States conducted a counterterrorism operation against a significant al Qaeda target in Afghanistan," a senior administration official said.
"The operation was successful and there were no civilian casualties," the official added.
It would be the first known over-the-horizon strike by the United States on an Al-Qaeda target in Afghanistan since American forces withdrew from the country on August 31, 2021.
The move may bolster the credibility of Washington's assurances that the United States can still address threats from Afghanistan without a military presence in the country.
On Saturday morning the Afghan interior ministry denied reports circulating on social media of a drone strike in Kabul, telling AFP a rocket struck "an empty house" in the capital, causing no casualties.
Taliban spokesman Zabihullah Mujahid tweeted that an" aerial attack" was carried out on a residence in the Sherpur area of the city.
Zawahiri, an Egyptian surgeon who became one of the world's most wanted terrorists, was identified as a mastermind of the September 11, 2001 attacks on the United States that killed nearly 3,000 people.
President Joe Biden on Monday said he hoped that the US killing of Al-Qaeda leader Ayman al-Zawahiri will help bring "closure" to families of those killed in the September 11, 2001, attacks.
"It is my hope that this decisive action will bring one more measure of closure," he said in a national address.
al-Zawahiri took over Al-Qaeda after Osama bin Laden was killed in Pakistan in 2011. The United States placed a $25 million bounty on al-Zawahiri's head.
His death raises questions about whether Zawahiri received sanctuary from the Taliban following their takeover of Kabul in August 2021.
This report was written with information sourced from Reuters and Agence France-Presse.