The US fell silent on Tuesday to remember the victims of the September 11 attacks, on the 11th anniversary of the atrocity.

Barack and Michelle Obama led remembrance services held across the country for the nearly 3,000 victims on three separate sites.

"It was a day like this one," said the President. "A clear blue sky, but a sky that would soon be filled with clouds of smoke and the prayers of a nation that was shaken to its core."

For the first time since the World Trade Center collapsed to the ground no politicians attended the memorial in Manhattan.

Instead, friends and family remembered the loved ones lost when extremists flew jets into the twin towers.

In Shanksville, Pennsylvania, where United flight 93 crashed after passengers revolted against their attackers, Secretary of Defense Leon Panetta renewed America’s promise.

"Nobody attacks the United States of America and gets away with it," he said.