US President Joe Biden on Sunday touted the killings of two Al-Qaeda leaders following the 9/11 attacks as he marked the 21-year anniversary of the attacks during a ceremony at the Pentagon.

“The enduring resolve of the American people to defend ourselves against those who seek us harm and deliver justice to those responsible for the attacks against our people has never once faltered,” Biden said, as quoted by The Hill.

“It took 10 years to hunt down and kill Osama bin Laden, but we did, and this summer I authorized a successful strike on [Ayman] al-Zawahiri,” he continued.

Al-Zawahiri, bin Laden’s deputy, took control of Al-Qaeda after bin Laden’s killing in 2011 and died in a US drone strike in late July.

Biden completed the US withdrawal from Afghanistan last summer, ending a roughly 20-year presence that began in 2001 shortly after the attacks.

The President has come under fire over the way the Afghanistan withdrawal was carried out, as the Taliban quickly regained control of the country after the US pullout. Biden has repeatedly defended his decision to withdraw from the country.

While former President Donald Trump has been one of the most vocal critics of Biden’s withdrawal, the move has also been criticized by senators from Biden's Democratic Party.

“Afghanistan is over, but our commitment to preventing another attack [against] the United States is without end,” Biden said in Sunday’s remarks at the Pentagon.

“Our intelligence, defense and counterterrorism professionals in the building behind me and across the government continue their vigilance against terrorist threats that [have] evolved and spread to new regions of the world,” he added.

Biden vowed to not hesitate and to disrupt terrorist activities “wherever they exist.”

“What was destroyed, we have repaired,” Biden said. “What was threatened, we fortified. What was attacked, an indomitable spirit has never, ever wavered.”