US President Joe Biden speaks at Joint Base Elmendorf-Richardson to mark the anniversary of the Sept 11, 2001, terrorist attacks, on Sept 11, 2023, in Anchorage, Alaska. (PHOTO / AP)

ANCHORAGE - US President Joe Biden urged Americans on Monday not to succumb to the "poisonous politics of difference and division" as he sought to revive the spirit of national unity after the deadly Sept 11, 2001, attacks 22 years ago.

"It shouldn't take a national tragedy to remind us of the power of national unity, but that's how we truly honor those we lost on 9/11," Biden told about 1,000 US military personnel at Joint Base Elmendorf-Richardson in Alaska.

Biden, his wife Jill, Vice-President Kamala Harris, her husband Doug Emhoff and US military commanders participated in separate events to remember those who died in the Sept 11 attacks and the war in Afghanistan that resulted.

On Sept 11, 2001, Islamist hijackers seized control of three jetliners and crashed them into the twin towers of New York's World Trade Center and the Pentagon, killing nearly 3,000 people. A fourth plane crashed into a field in Pennsylvania after passengers overcame the hijackers.

In this file photo taken on Sept 11, 2001, smoke rises from the burning twin towers of the World Trade Center after hijacked planes crashed into the towers, in New York City. (PHOTO / AP)

It shouldn't take a national tragedy to remind us of the power of national unity, but that's how we truly honor those we lost on 9/11 ... We must not succumb to the poisonous politics of difference and division. We must never allow ourselves to be pulled apart by petty manufactured grievances.

Joe Biden, US President

Biden's event took place in Alaska because he was on his way back from a five-day trip to India and Vietnam.

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His decision to hold the event in Alaska, instead of Washington or New York, was a departure from what has been presidential custom.

With 14 months to go until the 2024 presidential election, his remarks included a political message.

Biden decried what he called a "rising tide of hatred, extremism and political violence" in the United States. There is growing evidence that the country is grappling with the biggest and most sustained increase in political violence since the 1970s.

"We must not succumb to the poisonous politics of difference and division. We must never allow ourselves to be pulled apart by petty manufactured grievances," said Biden, recalling his friendship with John McCain, the late Vietnam war hero and Republican senator.

McCain, he said, put duty to country "above party, above politics, above his own person. This day reminds us, we must not lose that sense of national unity."

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Harris and other officials joined families of those who died at the 9/11 Memorial in New York, which occupies the footprints of the downed buildings.

New York Governor Kathy Hochul, Vice-President Kamala Harris and New York City Mayor Eric Adams attend the commemoration ceremony on the 22nd anniversary of the Sept 11, 2001, terrorist attacks on Sept 11, 2023, in New York. (PHOTO / AP)

"It's 22 years and this is the way I still feel, like it was yesterday," said Sybil Ramsaran, whose daughter Sarah died in the attacks.

Also at the New York event was Florida Governor Ron DeSantis, a candidate for the 2024 Republican presidential nomination.

Donald Trump, the leading Republican candidate for the 2024 race, issued a video vowing "we will never, ever forget" the 9/11 victims.

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Across the Potomac River from Washington, top US military leaders held their annual event at the Pentagon, and Jill Biden took part in a wreath-laying ceremony.

In Shanksville, Pennsylvania, Emhoff laid a wreath at the memorial for United Flight 93.

The attacks prompted then-president George W. Bush to launch a "global war on terror" that included a military assault on Afghanistan to find al Qaeda leader Osama bin Laden. Bin Laden eluded capture until he was killed in a US raid on his Pakistan compound in 2011 ordered by then-President Barack Obama.

The 9/11 attacks were the worst assault on US soil since the 1941 Japanese attack on Pearl Harbor, Hawaii, when 2,400 people were killed.