President Joe Biden joined Secretary of Defence Lloyd Austin and Joint Chiefs of Staff Gen Mark Milley at the Pentagon on Sunday to mark the 21st anniversary of the 9/11 terrorist attacks.
Nearly 3,000 people were killed when Al Qaeda terrorists hijacked four planes, crashing two into the World Trade Centre in New York City and one into the Pentagon outside of the nation's capital on September 11, 2001.
Passengers aboard the fourth plane managed to confront the hijackers, preventing further tragedy, but losing their lives when the plane crashed into a field in Shanksville, Pennsylvania.
Clad in a beige raincoat and accompanied by a marine holding a black umbrella, Mr Biden stood solemnly in the pouring rain outside the Pentagon.
President Biden told those gathered that 21 years after the worst terrorist attack in US history, the country remained unbowed.
“The American story itself changed that day. But while we did change, what we will not change, what we cannot change, what we never will, is the character of this nation that the terrorists thought they could wound,” President Biden said. “And what is that character? The character of sacrifice and love of generosity and grace of strength and resilience.”
The president, who at the time of the attack was a US senator, recalled a message that Queen Elizabeth II had sent to the American people in the direct aftermath of the attack.
“She pointedly reminded us, quote, ‘grief is the price we pay for love’,” he said.
The ceremony at the Pentagon was one of several held across the country, including at the site of the World Trade Centre in New York City, which was attended by Vice President Kamala Harris and her husband Doug Emhoff, and in Shanksville, Pennsylvania, where United Airlines flight 93 crashed.
First Lady Jill Biden, a Pennsylvania native, attended the event in Shanksville.
The events of September 11, 2001, changed the course of US and world history and sent America on a two-decade war footing that only came to an end when the last American troops flew out of Hamid Karzai International Airport in Kabul on August 31, 2021.
While the wars have finally concluded, Mr Biden said he remains committed to combatting terrorism and tracking down those responsible for the events of September 11.
He pointed to the recent killing of Al Qaeda leader Ayman Al Zawahiri as an example.
“We will not rest, we will never forget, we will never give up,” he said. “Our commitment to preventing another attack on the United States is without end.”