Al-Qaeda leader Ayman al-Zawahiri killed in drone strike in Afghanistan

The leader of al-Qaeda, one of the FBI's most wanted terrorists, was killed in a drone strike in Kabul over the weekend, President Joe Biden announced Monday night.

ABC News also confirmed through sources familiar with the operation that al-Qaeda leader Ayman al-Zawahiri was killed in the U.S. strike in Afghanistan. A senior administration official said earlier Monday that the U.S. conducted a successful counterterrorism operation against a "significant" al-Qaeda target, adding that there were no civilian casualties.

The counterterrorism attack took place in Wazir Akbar Khan, one of the wealthiest neighborhoods in Kabul and literally walking distance to the main diplomatic areas, including the U.S. Embassy. Al-Zawahiri was killed on the balcony of his safe house, a senior administration official said.

Biden delivered remarks on the operation Monday night, saying he authorized the U.S. strike that killed al-Zawahiri. The president also delivered a clear message to terrorism around the world.

"Justice has been delivered and this terrorist leader is no more," Biden said from the White House. "People around the world no longer need to fear the vicious and determined killer."

Biden said the United States is sending a clear message with this strike: "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."

The president said the intelligence community located al-Zawahiri earlier this year and that he moved to downtown Kabul. Biden said he gave the final approval "to go get him" after being advised that "the conditions were optimal."

"I authorized the precision strike that would remove him from the battlefield once and for all," he said, explaining that the operation was carefully planned to minimize the risk of harm to other civilians. Biden authorized the strike on July 25.

The president the mission was a "total success" because of the counterterrorism community, and key U.S. allies and partners.

Al-Zawahiri, who was born in Cairo in 1951, trained as a physician before founding the Egyptian Islamic Jihad, the FBI said. His organization had sought to overthrow the Egyptian government "through violent means" before merging with al-Qaeda between 1998 and 1999, the U.N. Security Council said.

As Osama bin Laden's al-Qaeda deputy, al-Zawahiri helped coordinate the Sept. 11, 2001, terror attacks that killed nearly 3,000 people in the United States, the U.S. Justice Department said.

Al-Zawahiri and bin Laden appeared together the day after the attacks in a video, in which an al-Qaeda spokesperson threatened the West, saying a "great army is gathering against you," U.S. officials said.

The Justice Department named al-Zawahiri and bin Laden as unindicted co-conspirators for their roles in coordinating the attacks.

Both had been indicted in the Southern District of New York in 1999 for the bombing of U.S. embassies in Kenya and Tanzania, which killed 224 people the previous year.

After bin Laden's death in 2011, al-Zawahiri took over as al-Qaeda's leader, officials said.

The FBI had placed al-Zawahiri, who was sometimes known as "The Doctor" or "The Teacher," on its list of Most Wanted Terrorists, offering a $25 million reward for his capture.

The strike that killed al-Zawahiri is a major success of U.S. counterterrorism efforts and the result of countless hours of intelligence collection over many years.

"This mission shows the tenacity and absolute dedication of U.S. intelligence and military professionals toward pursuing those responsible for the attacks of 9/11," said Mick Mulroy, retired CIA paramilitary operations officer and ABC News national security analyst.

"The message for al-Qaeda and its affiliates should be that the U.S. will never relent in its mission to hold those accountable who would seek to harm America and its people," Mulroy added.

It also "sends a resounding message to terrorist leaders and aspiring terrorists that America's resolve doesn't fade," said Eric Oehlerich, retired Navy SEAL commander and ABC News contributor, who also reiterated "that those who commit to harming the U.S. or American citizens will be held to account."

ABC News' Justin Ryan Gomez, Mick Mulroy, Eric Oehlerich, Martha Raddatz, Sohel Uddin and Kevin Shalvey contributed to this report.