Smaller ceremonies mark US attacks

Americans marked the anniversary of the September 11 2001 attacks with tearful messages to loved ones and moments of silence, but the smaller ceremonies gave a sense of moving on 11 years after nearly 3,000 people died in the worst terror attack in US history.

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

"Our country is safer, and our people are resilient," President Barack Obama said in a ceremony at the White House. He and first lady Michelle Obama laid a wreath at the Pentagon, above a concrete slab that said "September 11, 2001 - 937 am".

They later visited the graves of recent war dead from Afghanistan and Iraq at Arlington National Cemetery. The US military death toll years ago surpassed the 9/11 victim count.

Some said last year's 10th anniversary was a turning point for public mourning. For the first time, elected officials were not speaking at the New York ceremony.

Thousands had attended the ceremony in New York in previous years. This time, the crowd reached about 1,000 by late morning. A few hundred attended ceremonies at the Pentagon and in Pennsylvania.

As bagpipes played at the year-old September 11 memorial in New York, families bowed their heads in silence at 8.46am, the moment that the first hijacked jetliner crashed into the trade centre's north tower, and again to mark the crashes into the second tower, the Pentagon and a Pennsylvania field.

More than four million people have visited the memorial in the past year. On Tuesday, much of central Manhattan bustled like a regular weekday, except for clusters of police and emergency vehicles on the borders of the site.

Vice President Joe Biden attended a memorial service in Pennsylvania, where one of the hijacked airliners crashed in the fields of Shanksville. "No matter how many anniversaries ... the terror of that moment returns," he said.

At sunset, the Manhattan skyline was illuminated by twin towers of light, the annual Tribute in Light installation, which debuted six months after the attacks and has become a September 11 tradition.