Barack Obama has made an emotional return to Ground Zero to lay a wreath, days after the killing of Osama bin Laden.
The tribute at the site of the World Trade Centre was the focus of the president's visit to New York, arranged swiftly after the raid in Pakistan that culminated in the death of the al Qaida leader.
After laying the simple wreath of red, white and blue flowers at the foot of the Survivor Tree, which was damaged in the September 11, 2001 attack but later freed from the rubble, Mr Obama stood for a moment's silence.
He then hugged relatives of those killed in the terrorist atrocity, which was masterminded by bin Laden, and exchanged a few words with them.
Earlier, Mr Obama had visited a fire station in Manhattan which lost 15 men on September 11. He told firefighters that the shooting of bin Laden "sent a message around the world", that "when we say we will never forget, we mean what we say".
Speaking at the Engine 54, Ladder 4, Battalion, Mr Obama said the raid had transcended party politics, and promised the crews: "I just want to let you know that you are always going to have a president and an administration who has got your back."
A senior US defence official has admitted that only one of the five people killed in the operation was armed and fired shots.
Briefings earlier in the week by White House and Pentagon staff had portrayed the raid as involving prolonged and fierce firefights, with initial reports that bin Laden had fired a weapon. The unnamed official said the story had become clearer as the Navy Seal team were debriefed.
Mr Obama will meet some of those who were involved in the military operation when he visits Fort Campbell, Kentucky, on Friday, a White House official said.
Fort Campbell is home to the 160th Special Operations Aviation Regiment, which was involved in the raid against bin Laden.