New Delhi, Sept. 11 -- Americans are marking the 25th anniversary of the September 11 attacks, reflecting on the shock, the lives lost and the far-reaching impact of the al-Qaida attacks on key symbols of US power and prosperity.

Condoleezza Rice, who was serving as White House national security advisor on the day of the 9/11 attacks, said during a ceremony at the Pentagon that she continues to feel profound pain over the failure of those in positions of authority to recognise the threat in time to prevent the attacks.

Rice also expressed lasting personal remorse for the suffering endured by families of those killed and the trauma experienced by the country in the aftermath of the attacks.

"Those of us in authority on that day did not ...