Americans have marked the anniversary of the September 11 attacks, 11 years after nearly 3,000 people were killed in the worst terrorist incident in US history.

The commemoration was more subdued than in previous years, a reflection of the nation moving on after a decade of remembrance.

Hundreds gathered at the World Trade Center site in New York, the Pentagon and Shanksville, Pennsylvania, to read the names of the dead.

In a ceremony on the White House's south lawn, President Barack Obama said: "Our country is safer, and our people are resilient."

The President and First Lady then moved onto the Pentagon, where Michelle Obama laid a white floral wreath.

For the first time, politicians were not speaking at the New York ceremony. Fewer than 500 family members had gathered in Manhattan by Tuesday morning.

Vice President Joe Biden attended a memorial service in Pennsylvania, where one of the hijacked airliners crashed in the fields of Shanksville.