NEW YORKPresident Obama and first lady Michelle Obama arrived at Ground Zero this afternoon alongside former President George W Bush and his wife Laura. There they met families of victims, with all four warmly embracing them alongside plaques bearing the names of the dead.
The 10th anniversary ceremony began with the arrival of bagpipers and drummers and the singing of the national anthem by a youth chorus. But the world fell silent at 8.46am local time for a minute's silence to remember the horrific moment American Airlines Flight 11 hit the North Tower.
It was followed by President Obama's reading from Psalm 46, which begins, "God is my refuge and strength, a very present help in trouble".
New York mayor Michael Bloomberg then introduced the reading of the names of each of the 2,983 people who died in the attacks.
After the New York ceremony President Obama flew to rural western Pennsylvania to remember the sacrifice of those on United Airlines Flight 93.
ENGLANDMany of the families of the 67 British victims who died in the 9/11 attacks have attended services in London and New York.
Members of around 30 families who lost loved ones in the twin towers took part in a ceremony at the American Embassy in central London, while members of another 10 families took part in the service at Ground Zero.
Speaking at the service outside the US Embassy, the Prince of Wales said the families had to endure an "eternity of continuing, awful, agony".
"None of us will ever forget where we were or what we were doing when on that otherwise ordinary day, and out of a clear blue sky, came so much premeditated death and destruction on scale and in a way that shocked the entire world," he said.
"At the heart of those endless and rather impersonal news reports lay the shattered lives and hopes of all those who we join here today both in London and New York."
Ceremonies of remembrance also took place at Westminster Abbey and St Paul's Cathedral, while Mayor Boris Johnson unveiled a sculpted memorial, made from steel recovered from Ground Zero in Battersea Park, west London.