WASHINGTON — President Joe Biden announced Monday that al-Qaida leader Ayman al-Zawahri, a key plotter of the Sept. 11 attacks, was killed in a CIA drone strike he ordered targeting the terrorist leader in Afghanistan.

One of the world’s most wanted terrorists, al-Zawahri helped oversee the 2001 attacks on New York and the Pentagon, working closely with former al-Qaida chief Osama bin Laden, and had led the group over the last decade since bin Laden’s death.

The 71-year-old Egyptian was killed in a drone strike at 9:48 p.m. Eastern time Saturday at a residential location in Kabul, which fell to the Taliban a year ago almost immediately after Biden ordered the last U.S. forces to withdraw — a development that many feared would lead to more terrorist activity in Afghanistan’s capital.

“Justice has been delivered, and this terrorist leader is no more,” Biden said from the Blue Room balcony, as he remained in seclusion inside the White House residence after testing positive for the coronavirus in a rebound case. “No matter how long it takes, no matter how long you hide, if you are a threat to our people, the United States will find you and take you out.”

Afghanistan, Biden continued, “can’t be a launching pad against the United States. We’re going to see to it that won’t happen.”

A decade after Navy SEALs killed bin Laden during a daring raid on his heavily fortified compound on the outskirts of Abbottabad, Pakistan, al-Zawahri’s whereabouts had remained a mystery.

But U.S. intelligence officials, a senior administration official said, tracked al-Zawahri and his family to a safe house in downtown Kabul where they moved earlier this year. Over the next several months, officials observed al-Zawahri on a balcony, where he was eventually struck and killed in a plan devised to minimize the risk to his family and civilians in the heavily populated area.

Biden, the official said, was first briefed in April, received updates on the intelligence throughout May and June, and gave the final go-ahead for the attack after a meeting with top Cabinet and national security advisers on July 25, where all the participants expressed support for the mission.

Five days later, a drone carried out the attack, firing two Hellfire missiles at al-Zawahri on the balcony, killing him and him alone, according to the official. Unlike the operation targeting bin Laden, which lasted 40 minutes and ended with five people killed, including one of bin Laden’s sons, the drone strike was carried out without any U.S. military presence on the ground in Afghanistan — “carefully planned,” Biden said, to minimize collateral damage. “There were no civilian casualties,” he said, praising the intelligence officials who helped plan and execute the strike.

The Taliban was long aware of al-Zawahri’s presence in Kabul, the senior administration official said. They added that members of the Haqqani network, a terrorist group that is part of the Taliban government, whisked away the terrorist’s relatives shortly after the strike in an effort to hide their presence in the city.

The group’s harboring of al-Zawahri, the administration official added, amounted to a violation of the Doha agreement between the U.S. and the Taliban, under which the group agreed not to cooperate with terrorist groups.

Biden, long skeptical about the military’s commitment to the war in Afghanistan, famously cautioned President Barack Obama about the risks of the 2011 bin Laden raid when serving as vice president.

Ending the war there after 20 years of conflict was among Biden’s top first-year priorities, and he pushed ahead with the drawdown in the face of warnings from the Pentagon, scoffing at the potential for the country’s former government to fall to the Taliban just weeks before it did. The foreign policy debacle forced the White House to scramble to airlift thousands of vulnerable Afghans to safety, as a president who ran on experience and competency saw his approval drop.

The successful strike on al-Zawahri, Biden said, validated his own rationale for ending the U.S. presence in Afghanistan, which was predicated in part on a belief that counterterrorism operations could still be carried out without a permanent presence on the ground.

“I made the decision that after 20 years of war, the United States no longer needed thousands of boots on the ground in Afghanistan to protect America from terrorists who seek to do us harm,” the president said. “I made a promise to the American people that we would continue to conduct effective counterterrorism operations in Afghanistan and beyond. We’ve done just that.”

Senate Majority Leader Charles E. Schumer, D-N.Y., praised Biden for “decisive action that brings final justice to a loathsome mass murderer ... who helped orchestrate the cold-blooded murder of thousands of my fellow New Yorkers on 9/11.”

But several Republicans, while praising the intelligence officials involved, criticized Biden for last year’s messy pullout of Afghanistan, suggesting that al-Zawahri’s harboring by the Taliban in Kabul underscores how the situation there has made the world less safe.

“Our chaotic and deadly withdrawal from Afghanistan opened the door for al-Qaida to operate freely inside the country to conduct external operations against the United States and our allies again,” said Rep. Michael McCaul, R-Texas, the ranking GOP member of the House Foreign Affairs Committee.

In a statement, House Minority Leader Kevin McCarthy, R-Calif., called for a classified briefing “to discuss the resurgence of al-Qaida in the region over the past year.”

Biden, in his brief prime-time address to the country, reminded the nation of al-Zawahri’s central role in numerous al-Qaida attacks, including the 2000 bombing of the U.S. destroyer Cole in Yemen and of course Sept. 11.

Speaking to relatives of those killed in the attacks on the World Trade Center, the Pentagon and aboard United Flight 93 that crashed in Shanksville, Pa., Biden expressed hope that al-Zawahri’s death “will be one more measure of closure.”