With solemn tributes, the United States is marking the 10th anniversary of the September 11 terrorist attacks that killed nearly 3,000 people and launched the country into a decade of war.

President Barack Obama and his predecessor George W. Bush on Sunday morning toured the recently finished memorial at the site of the World Trade Center in New York City.

At 8:46 a.m. local time, New York City held a moment of silence observing the time the first plane struck the North Tower. Another moment of silence was observed at 9:03 a.m. to mark when the second plane struck the South Tower. Attendees at the ceremony also are pausing to mark when each of the towers fell.

Following the first moment of silence, President Obama read a Bible passage that speaks of God as refuge and strength. After the second moment of silence, former president Bush read a letter of support from then-president Abraham Lincoln to a mother who had lost all five of her sons in America's Civil War.

At the ceremony in New York City, family members and loved ones are reading the names of the thousands of people killed there a decade ago.

The Obamas travel on to Shanksville, Pennsylvania, for an observance of the crash of Flight 93. Later, they will travel to the Pentagon, just outside Washington, for a wreath-laying ceremony honoring the victims of the attack on the massive Defense Department building.

Sunday evening, Mr. and Mrs. Obama will attend a “Concert of Hope” in Washington .