Harrowing 9/11 photos reveal a charred Pentagon, a shell-shocked George Bush and a clock frozen in time as hijacked plane struck
It's been 16 years since the horrific al-Qaeda terror attacks shocked the world, leaving nearly 3,000 people dead
A CHILLING photograph of an office clock frozen in time features in a moving set of rarely seen photographs unveiled to mark the anniversary of the 9/11 terror attacks.
The clock's hands remain stuck just after 9.30am, which is when a gang of al-Qaeda hijackers plunged American Airlines flight 77 into the Pentagon killing all 64 people on board and 125 on the ground.
Two other planes American Airlines Flight 11 and United Airlines Flight 75 were crashed into the North and South towers of the World Trade Center complex in New York.
United Airlines Flight 93 then crashed into a field near Shanksville, Pennsylvania after the passengers took on the hijackers.
As America prepares to mark 16 years since the horror attacks - which left 2,996 people dead and more than 6,000 others wounded - the US Department of Defense has released the photos.
The powerful images include candid shots of then-President George Bush trying to take in what was happening to his seemingly untouchable country.
Other moving images show heroic firefighters sifting through building rubble in the search for survivors.
Two light beams shone in the early hours of this morning at the site of the World Trade Center attack in tribute to those who lost their lives.
Commemorations are being held across America, with President Donald Trump expected to speak at a ceremony for the 184 people killed at the Pentagon in Washington, DC.
Thousands of 9/11 victims' relatives, survivors, rescuers and others will gather at the World Trade Center later today to remember the deadliest terror attack on American soil.
President Trump and first lady Melania Trump will observe a moment of silence to mark the time the first plane hit.
He is also due to join a 9/11 ceremony at the Pentagon.
Defence Secretary Jim Mattis and Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, are hosting a private observance for victims' relatives there at 9.11am Monday.
Vice President Mike Pence and US Secretary of the Interior Ryan Zinke are to deliver remarks at the Flight 93 National Memorial near Shanksville.
Construction continues at the memorial, where ground was broken Sunday for a 93-foot tall Tower of Voices to honour the 33 passengers and seven crew members who died.
Meanwhile, rebuilding work continues at ground zero.
The third of four planned office towers is set to open next year; so is a Greek Orthodox church, next to the trade center site, that was crushed by the South Tower's collapse.
Work toward a $250 million performing arts centre continues after a design was unveiled last autumn.