New York, New York - New York commemorated the 25th anniversary of the devastating September 11, 2001 attacks Friday with a ceremony marked by controversy over President Donald Trump's absence and right-wing outrage over the attendance of the city's first Muslim mayor.

In an unusual move, Trump was paying his respects at the Pentagon, rather than joining the event in New York, where hijacked planes destroyed the World Trade Center and killed most of the 2,977 total victims on that world-altering day.

Vice President JD Vance and Trump's four living predecessors – Republican George W. Bush, who was in office during the attacks, and Democrats Joe Biden, Barack Obama, and Bill Clinton – were gathering at the Ground Zero site in lower Manhattan.

The ceremony, which began just after 8:40 AM (1240 GMT), was designed to be apolitical, with no speeches.

Bereaved family members read out the names of all those killed, with a bell tolling to mark major moments in the attack, which sparked years of US involvement in Middle East wars and bitter controversy over Washington's human rights record.

Terry Strada, widow of victim Tom Strada, unleashed a stinging attack on Saudi Arabia, accusing it of complicity in the attacks, and denouncing former presidents who were in attendance.

"You are missed more with each year that passes, but how can it be 25 years and still we have no justice for the role that Saudi Arabia played in your murder?" she said in unscripted remarks broadcast live worldwide.

The September 11, 2001 attacks were carried out by mostly Saudi hijackers orchestrated by mastermind Osama bin Laden, a wealthy Saudi.

Al-Qaeda meanwhile has marked the anniversary by releasing a video showing images of late leader Osama bin Laden and his son Hamza, who Trump said in 2019 had also been killed.

Ahead of the memorial, a drone show with 2,977 lights rose above New York Harbor, one for each person killed in the attacks.

Huge crowds were expected to gather in Lower Manhattan for the memorial service, and the Secret Service, which protects presidents, erected a security ring around the site of the 9/11 Memorial and Museum.

Alongside the former presidents was Democratic Mayor Zohran Mamdani, the Big Apple's first Muslim mayor.

He faced a well-organized campaign urging him to stay away, spearheaded by the right-wing New York Post newspaper and former mayor and Trump ally Rudy Giuliani.

A petition, which has gathered more than 100,000 signatures, accuses Mamdani of associating with unspecified individuals who are "dismissive of American institutions or insufficiently critical of extremist ideologies."

"It's concerning to me that the mayor is being treated differently simply because he is Muslim," city council member Shahana Hanif told CNN.

Mamdani won plaudits for recently revealing thousands of documents showing what city officials knew about toxicity levels of the air in Lower Manhattan following the attacks.

After the initial dust cloud that followed the collapse of the World Trade Center, months of pollution and lingering dust ensued, causing cancers from which thousands of New Yorkers still suffer today.