The CIA drone strike that killed al-Qaida leader Ayman al-Zawahri delivered a long-sought win for U.S. President Joe Biden's counterterrorism strategy, officials and experts have said, but also sharpened concerns about militants' presence in Afghanistan.

As the last U.S. troops and intelligence officers left Afghanistan last August after 20 years of war, Biden shifted to an "over-the-horizon" strategy of relying on drones and spy planes to track and hit al-Qaida and Islamic State militants inside the country.

The CIA strike on Sunday in downtown Kabul, the first publicly known one of its kind since the pullout, gives Biden a rare accomplishment less than a month from the anniversary of the chaotic exit that saw the Taliban regain power, 13 U.S. troops killed and tens of thousands of at-risk Afghans left behind.