WASHINGTON: The United States (US) on Sunday marked the 21st anniversary of the Sept 11, 2001 terror attacks, during which roughly 3,000 people were killed when al-Qaeda hijackers struck the financial and political capitals of the US.

"21 years ago, 21 years, and we still kept our promise. Never forget. We'll keep the memory of all those precious lives stolen from us," Anadolu Agency (AA) quoted President Joe Biden as saying during an event at the Pentagon.

Besides the event at the Pentagon, where 184 people were killed after a hijacked American Airlines plane crashed, ceremonies were held at Ground Zero, New York, where World Trade Centre's twin towers were destroyed, and Shanksville in the US state of Pennsylvania.

Vice President Kamala Harris and husband Doug Emhoff joined the observance at Ground Zero, while first lady Jill Biden was in Shanksville to mark the anniversary of the 9/11 terror attacks.

During all three observances, the names of the victims were read.

"America itself changed that day. But what will not change, and never will, is the character of this nation that the terrorist thought they could wound.

"We raised monuments and memorials to the citizens whose blood sacrificed on this (Pentagon) ground and then Shanksville, and Ground Zero, to keep touch of the memory, keep it bright for all the decades to come," he added.

In his remarks, the US president also touched on the unity of the nation, saying: "We also had to face down the worst impulses, fear, violence, discrimination directed against Muslim Americans, as well as Americans of Middle Eastern and South Asian heritage."

"There's nothing this nation cannot accomplish when we stand together and defend with all our hearts. That was what makes us unique in the world," Biden said.

Al-Qaeda leader Osama bin Laden claimed responsibility for the coordinated attacks.

-- BERNAMA