The president joined Americans around the country, and particularly at the three sites of the terrorist attacks, in remembering the day. After the moment of silence, Mr. Obama travelled to the Pentagon to place a wreath and speak at the site where a hijacked plane hit that building.
"In pursuit of al-Qaida and its extremist allies we will never falter," he said.
Listen to the President's full remarks here:
In New York, Vice President Joe Biden and Mayor Michael Bloomberg, among others, joined the families of victims to read the names of those killed at the World Trade Center, stopping for moments of silence at 8:46 am and 9:03 am, the times the two planes hit the towers.
Representatives of volunteer groups such as the American Red Cross and the United Way joined family members in reading the names.
The president and Mrs. Obama were planning to take part in a community service event Friday afternoon. The president this year designated Sept. 11 a "national day of service" in an effort to encourage people to mark the day through community service and volunteering.
"From this day forward, we will safeguard the memories of those who died by rekindling the spirit of service that lit our city with hope and helped keep us strong," Bloomberg said at the New York ceremony. "Eight years ago, countless people played a part in history by doing something to help another person . . . Each act was a link in a continuous chain that stopped us from falling into cynicism and despair."
But some family members told the Associated Press they worried a emphasis on volunteerism would detract from the focus on remembrance.
---- Compiled from wire reports and other media sources