Obama then flew on to lay wreaths at the crash site of Flight 93 in Pennsylvania and at the Pentagon outside Washington.
At a ceremony in Washington later Sunday Obama told Americans “we can never get back the lives we lost on that day, or the Americans who made the ultimate sacrifice in the wars that followed.”
But “these past 10 years have shown that America does not give in to fear,” the US president stressed.
He added that “nothing can break the will of a truly United States of America,” and cast the fight against terrorism as victory alongside some of his nation’s greatest achievements.
At Ground Zero, the Stars and Stripes fluttered from cranes used in the massive project to rebuild the World Trade Center, while below, relatives of the 2,977 victims of the attacks brushed fingertips across the names of their loved ones etched in bronze around a new memorial.
With federal officials warning of a new terrorism scare, lower Manhattan was under police lockdown. Security in other major cities was also tight, as Obama called for a “heightened state of vigilance.”
The ceremony began in New York with a procession of bagpipers and singing of the national anthem, before a bell signaled the first of six moments of silence marking the times when the four hijacked airplanes hit their targets and the Twin Towers collapsed.
The sky over the Big Apple was initially clear, recalling the backdrop to the horrific surprise attack on the World Trade Center, where 2,753 of the day’s victims, including 343 firefighters, died in the inferno of collapsing skyscrapers.
As every year since September 11, 2001, relatives of the dead took turns reading out the names, a heartbreaking litany accompanied by virtuoso cellist Yo-Yo Ma.
Readers fought to keep emotions in check as they pronounced loved ones’ names. “I’ve stopped crying, but I haven’t stopped missing my dad. He was awesome,” one young man said.
“From the depth of my soul,” a sobbing woman called out to her deceased husband, “we will always miss you.” The ceremony ended nearly five hours later with the playing of “taps” by uniformed buglers.
Reflecting a growing sense that it is time to turn a corner from 9/11, the Ground Zero ritual this time was accompanied by signs of optimism.
Instead of the chaotic-looking construction site and vast pit that scarred lower Manhattan for years, the ceremony now features a gleaming, three-quarters-built One World Trade Center tower and other signs of progress.
Sunday also saw the dedication of a simple, but moving monument consisting of fountains sunk into the footprints of the former towers, with the names of the dead inscribed around the edges.
The president, who also declared “Al-Qaeda is on the path to defeat,” visited Shanksville, Pennsylvania, site of the crash of Flight 93.
The 40 victims of that hijacking have often been overlooked in the bigger dramas of the strikes on the Pentagon and the Twin Towers. But they were remembered Sunday as heroes for overpowering their assailants, crashing the plane before its apparent target of nearby Washington.
Obama’s also stopped at US military headquarters where earlier Vice President Joe Biden attended a ceremony honoring the 184 people who died when a hijacked airliner smashed into the exterior of the Pentagon complex.
In the evening, about 2,000 people, including victims’ relatives, politicians and religious leaders, packed the Kennedy Center in Washington for 90 minutes of music and remembrance.
The concert, which was organized by the National Cathedral was relocated to the Kennedy Center due to an accident at the cathedral site.
“Nothing can break the will of a truly United States of America,” Obama told the gathering.
The 9/11 remembrances unite Americans like almost no other event. According to a poll last week, 97 percent of people remember where they were when they heard the news, on a par with John F. Kennedy’s assassination.
This year’s event also follows the stunning news in May that US Navy SEALs had flown into Pakistan and shot dead Al-Qaeda founder Osama bin Laden.
Yet while Al-Qaeda is severely weakened and New York is recovering physically, the anniversary still finds a nation struggling to overcome the longer-term impacts of the last decade, including a stumbling economy and an over-extended military.
There was also a reminder of the jumpiness within the United States on Sunday when two fighter jets were scrambled to shadow an airliner headed to New York after reports of passengers locking themselves in the toilet. However, the incident ended without trouble and “there’s no indication of a terrorist attack,” a US defense official said.