NEW YORK (AP) - Solemnly honoring victims of the Sept. 11 terror attacks, President Barack Obama hugged survivors, thanked the heroes of one of the nation's darkest days and declared Thursday that the killing of Osama bin Laden after all these years was an American message to the world: "When we say we will never forget, we mean what we say."

On a brilliant blue-sky day, one of reflection more than celebration, Obama offered New Yorkers a moment of their own. Standing at the gritty construction site of ground zero, where the towers fell and a memorial now rises, the president laid a wreath of red, white and blue flowers for the nearly 3,000 who died as he marked a turning point for the nation and this city of steely resilience.

For Obama, the day was about the importance of being in New York in the aftermath of the successful raid to find and kill bin Laden, the al-Qaida leader. Obama addressed families who have watched and wondered for nearly a decade whether the government would track down its most infamous enemy.

On this special ground, Obama never mentioned bin Laden's name.

Still, this was where the terrorist inflicted his greatest damage on a similarly sunny day in 2001 when hijacked airliners were crashed into the World Trade Center. Nearly 200 other people died when a third airliner hit the Pentagon - Vice President Joe Biden led a ceremony there on Thursday, and Bush Defense Secretary Donald Rumsfeld attended - and others were killed when yet a fourth plane crashed in Pennsylvania.

Enthusiastic, emotional New Yorkers waited on streets to see the president, but there were few displays like the more raucous exuberance of a few days earlier. There were happy faces, shouts of "USA! USA!" and flags waved in the crowd, but there also was heavy security and most people were cordoned off blocks from where the president could be seen.

Referring to the daring U.S. raid to take down bin Laden in Pakistan, Obama said of all those who died on Sept. 11: "It says we keep them in our hearts. We haven't forgotten."

Days after the attacks, President George W. Bush stood here with firefighters and a bullhorn. There was a different feel a decade later as another president paid his respects. Obama met with firefighters, then police, before having a solemn moment at ground zero and meeting privately with families of those who died.

"This is a symbolic site of the extraordinary sacrifice that was made on that terrible day," the president said at Engine 54, Ladder 4, Battalion 9. The firehouse in New York's theater district lost 15 firefighters on 9/11. The fire crews gave him hearty applause.

Obama said the American pursuit of the terrorist leader "sent a message around the world but also sent a message here back home that when we say we will never forget, we mean what we say, that our commitment to making sure that justice is done is something that transcended politics, transcended party."

Bin Laden was shot dead in a raid on his Pakistan compound early Monday in Pakistan, the result of years of painstaking intelligence work and a covert military mission in which none of the U.S. commandos was killed.

The president closed his eyes and clasped his hands at the outdoor memorial where the twin towers of the World Trade Center once dominated the Manhattan skyline.

60 stories high. Mammoth fountains and reflecting pools mark the footprints of the fallen towers. Now the nearby skyline is filled with construction machinery. The emerging skyscraper informally known as Freedom Tower is more than

Obama spoke with children who lost parents and adults who lost spouses. As he bowed his head, a jetliner screamed by, far overhead.

The president also peppered his brief comments with reminders of the challenges ahead, and his call for a new spirit of national unity.

It wasn't a moment for celebrating the military operation that killed bin Laden; that may come Friday, when the president visits Fort Campbell, Ky., home to the Army unit involved in transporting Navy SEALS in and out of bin Laden's compound. White House officials said Obama intended to privately thank participants in the raid.

Obama said Thursday he hoped the results of the raid on bin Laden's compound showed that "we did what we said we were going to do, and that Americans, even in the midst of tragedy, will come together, across the years, across politics, across party, across administrations, to make sure that justice is done."

Former New York Mayor Rudy Giuliani, who led the city in the days after the attacks, joined Obama during the day.

Obama invited Bush to join him Thursday in New York, but the former president declined.

Obama's visit came as new details emerged of the operation on bin Laden's Pakistan compound.

A senior defense official said Thursday that only one of the five people killed in the raid was armed and fired a shot - an account that differed from original administration portrayals of an intense firefight. The White House also now says bin Laden was unarmed when he was shot, after officials initially said the terrorist was holding a gun or even firing.

Obama also addressed bin Laden's burial at sea, saying in an interview with CBS' "60 Minutes" that: "Frankly, we took more care on this than, obviously, bin Laden took when he killed 3,000 people."

Such details perhaps mattered little to New Yorkers who suffered most grievously in the attacks and are now deeply gratified to see bin Laden's demise.

Ahead of Obama's arrival, Deanne McDonald stood at the northeast corner of the World Trade Center site waving an American flag in each hand and shouting "Obama got Osama! Obama got Osama!"

"God bless the Navy SEALS," said McDonald, 38, from Brooklyn. She took work off on Thursday to wait for the president, saying she was prouder than ever to be an American.