Dignitaries arrived at the World Trade Center site in lower Manhattan for the 20th anniversary memorial for the September 11, 2001 attacks.
More than 2,600 at the World Trade Center were killed, as well as 125 people who died at the Pentagon and 265 on the four airliners involved in all the attacks.
Among the early arrivals at the ceremony site were former U.S. President Barack Obama, current U.S. Attorney General Merrick Garland and former New York City Mayor Rudolph Giuliani.
President Joe Biden will commemorate the 20th anniversary of the Sept. 11 attacks on the United States on Saturday by visiting each of the sites where hijacked planes crashed in 2001, seeking to honour the victims of the devastating assault.
Biden will begin the day in New York, where he will attend a ceremony at 8:30 EDT at the site where the World Trade Center’s twin towers once stood before planes struck the two buildings and caused them to collapse.
Then he will travel to Shanksville, Pennsylvania, where United Flight 93 crashed into a field after passengers overtook the hijackers and prevented another target from being hit.
Finally, Biden will return to the Washington area to visit the Pentagon, the symbol of U.S. military might that was pierced by another of the planes that were used as missiles that day.
9/11 attacks changed the world order on so many levels
The anniversary comes shortly after the end of the U.S.-led war in Afghanistan, launched some 20 years ago to root out al Qaeda, which carried out the 9/11 attacks.
Biden’s withdrawal of U.S. troops in August, months after a deadline set by his Republican predecessor, Donald Trump, and the resulting rapid fall of the country to the Taliban has drawn criticism from members of both political parties.
Biden is not scheduled to deliver remarks at any of the sites, but he released a video on Friday to express his condolences to the loved ones of the victims and highlight the national unity that resulted, at least initially, after 9/11.
Biden, a Democrat, pledged to build up such unity after he came into office earlier this year, but the country remains deeply divided politically.
U.S. presidents often travel to one of the three attack sites on the 9/11 anniversary but it is unusual to go to all three of them on the same day.
Last month, many families of 9/11 victims asked Biden to skip 20-year memorial events unless he declassified documents they contend will show Saudi Arabian leaders supported the attacks. Last week the president ordered the Department of Justice to review documents from the FBI probe into the attacks for declassification and release.