'Never, ever forget' - America marks 25th anniversary of 9/11 attacks
In New York, the Pentagon and Pennsylvania, solemn ceremonies commemorate the landmark anniversary.
'Never, ever forget' - America marks 25th anniversary of 9/11 attacks
Twenty-five years on from 9/11, current and former US presidents have paid tribute to the people killed when terrorist hijackers flew planes into the World Trade Center, the Pentagon and a field in Pennsylvania.
President Donald Trump led a ceremony at the Pentagon, while US Vice-President JD Vance joined a remembrance event at the World Trade Center site in New York, alongside all four living former US presidents and first ladies.
Moments of silence were observed at the times of the attacks, and the names of almost 3,000 victims were read aloud.
Commemorations also took place in Shanksville, Pennsylvania, where Flight 93 went down after passengers fought the hijackers.
US Commerce Secretary Howard Lutnick lost his brother Gary and several colleagues in the attack
President Trump spoke at the Pentagon
George W Bush, who was president when the attacks happened, was joined by former Presidents Joe Biden, Barack Obama and Bill Clinton at Friday's ceremony.
At the Pentagon, Trump attended the commemoration with cabinet secretaries and Condoleezza Rice, who was US secretary of state on 9/11.
"Today we renew the sacred oath that we first swore in their names a quarter of a century ago," Trump said. "We will never, ever forget. That's why we fight today."
He tried to connect the "war on terror" that followed 9/11, which led to years of US involvement in Middle East wars, with his present conflict in Iran.
Trump told the crowd that the Islamic Republic "will never, ever have a nuclear weapon".
Janice Brooks had moved to New York only a couple of weeks before 9/11 to start what she calls "the biggest adventure", working for a company on the 84th floor of the South Tower of the World Trade Center.
She told the BBC she was in the office when the first plane struck the North Tower. As she was evacuating, the second plane hit with an "almighty thud".
Brooks said she heard "one of those horror film screams" as a woman was struck by debris. She looked up and saw a "big gaping hole" where her office should have been.
Every year on 11 September, bells ring to mark the exact time each of the four planes crashed, and the exact time the Twin Towers fell.
Each of the six bells is followed by a moment of silence.
This year, a seventh bell was rung to remember the thousands who died from diseases including cancer after the attacks.
Illnesses linked to dust and smoke from the towers' collapse have since killed more than three times the nearly 3,000 people who died in the attacks, US health officials say.
As the names of the dead were read for nearly four hours at the Manhattan ceremony, a 9/11 widow criticised Saudi Arabia and what she described as failures by US officials to hold the kingdom accountable.
"You are missed more with each year that passes," Terry Strada said of her husband Tom Strada in remarks broadcast live worldwide.
"But how can it be 25 years and still we have no justice for the role that Saudi Arabia played in your murder?"
The comment by Mrs Strada, national chairperson of 9/11 Families United, drew applause from the audience.
Most of the hijackers who carried out the 9/11 attacks were from Saudi Arabia, and planning was led by al-Qaeda founder Osama Bin-Laden, scion of a prominent Saudi family.
But Saudi officials have repeatedly denied any involvement in the terrorist attacks, and in 2004 the 9/11 Commission Report cleared the country of any involvement.
Events were also held elsewhere to honour the victims. In London, there was a ceremonial event at Buckingham Palace attended by Foreign Secretary Ed Miliband and the US ambassador Warren Stephens.
The Toronto Stock Exchange also held an event to remember colleagues who died in the attacks.
Commemorations were held at Lloyds of London
In Milan, a group of Italian and US firefighters took part in a ceremonial stair climb to honour the emergency responders who died in the line of duty.
Wearing their uniforms and carrying equipment, they climbed 110 floors up and down the Galfa Tower, in remembrance of the number of storeys on each of the Twin Towers.