New York is marking the ninth anniversary of the September 11 attacks on the United States with a ceremony close to Ground Zero, the former site of the World Trade Centre.
Commemorations are also taking place at the Pentagon and in Shanksville, Pennsylvania, which were also hit by hijacked airliners.
As many as 3,000 people lost their lives in the coordinated destruction.
President Barack Obama attended a service at the Pentagon, which was struck by a Boeing 757 30 minutes after the Twin Towers were assaulted:
“As Americans we are not and never will be at war with Islam. It was not a religion that attacked us on that September day, it was al Qaeda, a sorry band of men which perverts religion. And just as we condemn intolerance and extremism abroad, so will we stay true to our traditions here at home as a diverse and tolerant nation”.
The remembrances are taking place against a backdrop of a row over an Islamic centre close to Ground Zero and a extremist pastor who has threatened to burn copies of the Koran.