Relatives of September 11 victims have appealed to presidential candidates Kamala Harris and Donald Trump for accountability as the US marked an anniversary of the terror attacks laced with election-season politics.

President Joe Biden, former president Mr Trump and Vice President Kamala Harris stood together at ground zero just hours after the Republican and Democrat rivals faced off in their first debate.

Mr Trump and Mr Biden — the successor whose inauguration Mr Trump skipped — shook hands, and former New York mayor Michael Bloomberg appeared to facilitate a handshake between Ms Harris and Mr Trump.

Then the presidential rivals stood only a few feet apart, Mr Biden and Mr Bloomberg between them, as the observance began with the tolling of a bell and a moment of silence. At Mr Trump’s side was his running mate, Senator JD Vance.

The image was one of putting politics aside at another solemn commemoration of the hijacked-plane attacks that killed nearly 3,000 people on September 11 2001.

For years, politicians have been only observers at ground zero commemorations, the microphones going instead to relatives who read victims’ names aloud.

Michael Bloomberg, Republican presidential nominee former President Donald Trump and Republican vice presidential nominee JD Vance attend the 9/11 Memorial ceremony
Donald Trump and his running mate JD Vance were at the ceremony (AP)

Some of those readers took the occasion on Wednesday to deliver political messages of their own.

“We are pleading for your help, but you ignore us,” Allison Walsh-DiMarzio said, directly challenging Mr Trump and Ms Harris to press Saudi Arabia about any Saudi official involvement in the attacks.

Most of the 19 hijackers were Saudi but the kingdom denies involvement by senior Saudi officials.

“Which one of you will have the courage to be our hero? We deserve better,” Ms Walsh-DiMarzio said. She is a daughter of 9/11 victim Barbara Walsh, an administrative assistant.

A New York Police Department honour guard holds an American flag
The ceremony took place at ground zero in New York City (AP)

Joanne Barbara was one of multiple readers who spoke out against a now-revoked plea deal that military prosecutors struck with alleged 9/11 mastermind Khalid Sheikh Mohammed and two fellow defendants.

“It has been 23 years, and the families deserve justice and accountability,” said the widow of assistant fire chief Gerard Barbara.

Mr Biden, on his last September 11 in office, and Ms Harris paid respects on Wednesday at all three places where commercial jets crashed after al Qaida operatives seized them on 9/11.

After the ground zero commemoration, the pair laid wreaths, spoke to victims’ families and walked through the fields of the expansive Flight 93 National Memorial near Shanksville, Pennsylvania, before heading to the Pentagon.

Mr Trump and Mr Vance moved on from ground zero to visit a New York City fire station.

A police chief places flags of remembrance on the memorial
The atrocity took the lives of many emergency workers (AP)

The attacks killed 2,977 people and left thousands of bereaved relatives and scarred survivors. The planes took down the World Trade Centre’s twin towers and carved a gash in the Pentagon, the US military headquarters.

While it may seem that many Americans do not observe 9/11 anniversaries any more, “the men and women of the Department of Defence remember,” Defence Secretary Lloyd Austin said on Wednesday.

The attacks altered US foreign policy, domestic security practices and the mindset of many Americans who had not previously felt vulnerable to attacks by foreign extremists.

Effects rippled around the world and through generations as the US responded by leading a “global war on terrorism”, which included invasions of Afghanistan and Iraq. Those operations killed hundreds of thousands of Afghans and Iraqis and thousands of American troops.