The United States has marked the sixth anniversary of the 11 September 2001 attacks with a series of tributes.

In New York, the families of those who died after two planes ploughed into the World Trade Center paid their respects once more.

Punctuated by silences to mark the moments when the planes hit and the towers collapsed, the names of the 2,749 victims were read out by rescue workers.

For the first time, much of the ceremony was held away from the World Trade Center site, where construction work is under way on four new towers.

President George W Bush, who has previously laid a wreath at Ground Zero, this year held a ceremony at the White House.

Another memorial was held at the Pentagon, where 184 people died when a plane was flown into the building.

Families also gathered in Shanksville, Pennsylvania, to remember the 40 passengers and crew who lost their lives when hijackers brought down United Airlines Flight 93.

The anniversary was also marked by US forces serving in Afghanistan and elsewhere.