New York: Americans marked the seventh anniversary of the September 11, 2001, terrorist attacks with a heartfelt ceremony at Ground Zero and other solemn remembrances around the country, honouring those killed in the strikes that ended the US's sense of invulnerability and set the stage for two wars.

Relatives of victims killed at the World Trade Centre gathered at Ground Zero in lower Manhattan for readings from dignitaries and a recitation of the names of the dead.

Later yesterday, presidential candidates Barack Obama and John McCain were due at ground zero to pay silent respects.

In all, almost 3,000 people from over 90 countries were killed in the separate attacks on three sites in the United States.

In Washington, Bush led a White House gathering in observing the moment which served to shape his presidency.

Tragedy

Standing next to him for the brief South Lawn ceremony were his wife, Laura, and Vice-President Dick Cheney and his wife, Lynne.

"Today marks the seventh anniversary of the day our world was broken," New York City Mayor Michael Bloomberg said. "It lives forever in our hearts and our history, a tragedy that unites us in a common memory and a common story ... the day that began like any other and ended as none ever has."

The ceremony at Ground Zero included moments of silence at 8.46am and 9.03am - the times that two hijacked jets slammed into the twin towers. Two more moments of silence were to be held at the times the towers fell. Services were also being held in Pennsylvania and at the Pentagon, where a new memorial will be dedicated.

The assembled crowd in Washington numbered in the hundreds and included leaders of Congress, members of the Cabinet, diplomats, men and women in military uniform and chefs, plumbers, ushers and others who work at the White House. Across the Potomac River, a new memorial at the Pentagon was dedicated as the names of the victims were read aloud to mourners there.

Pledge

Gordon England, deputy secretary of defence, said at the Pentagon: "Today as we dedicate this memorial, we also dedicate ourselves to never forget what happened here, and we make a solemn pledge to never again let this happen in America."

"God bless the fallen, their families and all who sacrifice for freedom and liberty," England said.

On one side of a Pentagon parking lot, nearly 3,000 flags flew to mark all the lives lost on that day.

The attacks, claimed by Al Qaida, paved the way for Bush - then less than a year into his first term as president - to launch an attack against Afghanistan, where the terror group's leader Osama Bin Laden was hiding. They also served as justification for the attack on Iraq, which led to the toppling of Saddam Hussain's regime.

Bush also was to go to the Pentagon to dedicate the memorial featuring 184 benches over small reflecting pools, representing each life lost when American Airlines Flight 77 flew into the symbol of US military might on that clear and sunny September morning.