The United States has honoured the victims of the 9/11 terrorist attacks with official ceremonies at Ground Zero in New York, at the Pentagon in Virginia and Shanksville in Pennsylvania.
Nearly 3000 people died when four hijacked planes were crashed in 2001.
Mourners filed into a new memorial at Ground Zero, where a decade ago the 110-storey skyscrapers of the World Trade Center collapsed.
President Barack Obama and his predecessor, George W Bush, stood together as they attended the main ceremony at Ground Zero.
At the Pentagon, US Vice President Joe Biden paid tribute to the armed forces and intelligence services.
He said the attack was an unconscionable tragedy but spoke of a new generation of patriots being galvanised by terrorists who had tried to shatter the symbolism of US military might.
A ceremony was held at Shanksville in Pennsylvania, where one of the hijacked planes crashed into a field following a struggle between terrorists and passengers.
Relatives wept as the names of victims were read out, and a minute's silence marked each moment a jet struck and when the two towers came down.
Ceremonies have also taken place in some of the 100 countries whose citizens died in the attacks.
Prince Charles and British Prime Minister David Cameron joined relatives of the 67 Britons who died in the attacks at a remembrance ceremony in London, the BBC reports.
Services have also taken place in Glasgow, Birmingham and Belfast.
A former Radio New Zealand reporter who was in Manhattan on the day of the attack says memories are still raw.
Rae Lamb, who was Radio New Zealand's health correspondent at the time, says she will never forget the initial sense of disbelief when she first heard a plane had flown into a World Trade Center tower.
