Thousands of people observed moments of silence in Ground Zero in New York and witnessed the dedication of a memorial for 9/11 victims in Pentagon as President George W Bush [Images] said the US "will always grieve" the victims of the terror strike that shook the world seven years ago.

Relatives of those killed at the World Trade Center [Images] gathered at Ground Zero in lower Manhattan to hear readings from dignitaries and a recitation of the names of the dead.

Two moments of silence were observed at 8:46 am and 9:03 am, when the hijacked jets struck the Twin Towers of the WTC. Later, presidential candidates Barack Obama [Images] and John McCain [Images] were due there to pay silent respects.

In all, almost 3,000 people from over 90 countries were killed in the terror attacks on Pentagon and New York on September 11, 2001. A fourth hijacked plane crashed in a field in Pennsylvania.

A sailor rang a bell for each of the 184 victims of the attack on the Pentagon. Amid tunes of bagpipes, relatives of the victims and dignitaries watched as a flag was raised over the memorial.

The Pentagon Memorial will stand as an everlasting tribute to the innocent souls who perished on these grounds, Bush said and added that since that fateful day seven years ago, American troops have taken the fight to the terrorists abroad "so we do not have to face them here at home".

"The benches here bear each of their (victims) names. And beneath each bench is a shimmering pool filled with the water of life, a testament to those who were taken from us and to their memories that will live on in our hearts," Bush said.