America Marks 10th Anniversary of 9/11 Attacks

"My big brother, Joseph Michael Ciccone, we love you and miss you," one speaker said. "It's 10 years, but it's still not easy. Your family loves you and misses you."

"She wanted to work for justice but died from injustice," Tanya Garcia said of her 21-year-old sister, Marlyn, a graduate of NYC's John Jay College of Criminal Justice who died while working at Marsh & McLennan Cos., a financial services firm that lost 295 employees and 63 contractors in the attack. "She was a victim of horrendous terrorism."

New York City Mayor Mike Bloomberg opened the ceremony with the first city-wide moment of silence at 8:46 a.m. to commemorate the moment when American Airlines Flight 11 struck the North Tower. Obama then read from Psalm 46, which starts, "God is our refuge and strength."

The ceremony also included performances by Yo-Yo Ma, James Taylor and Paul Simon.

Among the crowd gathering at the memorial plaza this morning were children too young to have been alive 10 years ago, clutching Teddy bears and wearing dresses with flags sewn into them, family members wearing T-shirts with the words "Never Forget" emblazoned on them, and T-shirts commemorating members of those fire department ladder units and police precincts who perished in the attack.

Mario Montoya came to remember his best friend, Harry Ramos, who worked on the 82nd floor of the North Tower.

"Every year, I come here to feel closer to him," Montoya said.

Police and security presence at the memorial and throughout Lower Manhattan remained significant; police dogs and armed guards were present throughout the ceremony. New York City police commissioner Raymond Kelly told ABC News that there was no new information on a suspected terror plot, but "no reason to lessen our alert status."