US President Barack Obama and his wife Michelle along with former President George Bush and his wife Laura led the world in mourning the loss of nearly 3,000 people, who lost their lives exactly 10 years ago in the most fearful terror attack that changed the way we live.
Dressed in black, the two couples held hands as they walked slowly along the memorial, watching the wall etched with names of the 2,983 people killed in the terror unleashed by al-Qaeda chief Osama bin Laden.
Even though bin Laden was taken out in unilateral raid by American military commandos on May 2 in Pakistan, the wounds of the victim's families, including Indians, remained fresh.
An eerie silence gripped the ground-zero as the America's first family along with Bush spent about a minute at the 30-foot waterfalls that are part of the new memorial.
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People silently held on to American flags as well as photos of their loved ones who died when hijacked twin planes rammed into the iconic World Trade Centre here, bringing the skyscrapers down like a pack of cards.
The ceremony began with a procession of bagpipers and singing of the national anthem by a choir.
Tears rolled down the cheeks of many present as names of the victims were read out at the event, which was under heavy security cover, following fresh security alerts regarding a possible al-Qaeda attack.
Families could be seen clutching each other's hand as Obama read out verses from Biblical chapter Psalm 46, which talks about God as a source of refuge and strength.
Mayor Michael R Bloomberg said that the attacks had turned "a perfect blue-sky morning" into "the blackest of nights."
He added, "We can never unsee what happened here."
Incidentally, unlike earlier occasions, the ritual of reading the names of the dead took place against a backdrop of the spectacular, three-quarter-built 1 World Trade Center tower, rather than a construction site- ground-zero.
People also saw the dedication of a simple, but moving monument consisting of massive fountains, sunk into the footprints of the former towers, with the names of the dead written in bronze around the edges.
People gathered and prayed at cathedrals in their cities and laid roses before fire stations.
Americans saw new memorials in lower Manhattan, rural Pennsylvania and other places.
Formal ceremonies were held in many countries to remember the souls of those killed.
Even though 10 years have passed since the tragic attack, the pain and the suffering still exists.
Indian origin surgeon John Mathai, who lost his younger brother Joseph, says 10 years may seem a long time to many but for him the years have not dulled the pain of the "unfortunate" event.
"The loss of my brother is a loss that will never be replaced. Ten years have gone by but there has hardly ever been a day where I have not thought of him and the wonderful time we spent in New York," Mathai said.
New Jersey resident Arjan Mirpuri's 30-year-old son Rajesh was among victims.
"My son did not even work at the World Trade Centre. He had gone there that day to attend a trade show. Before that day, Rajesh had never gone to the WTC. 9/11 became the most unfortunate day of our lives," Mirpuri told PTI.
And it is not that the threat of a terror attack has decreased since then. Even as the world pause to reflect on the tragedy that killed people from more than 90 countries, the city and Washington is under intense security gaze.
Meanwhile, remembrance services were held across Britain for those who died in the attacks, which included 67 Britons.
In London, families of some of the 67 British victims gathered for a service at Grosvenor Chapel and a ceremony was held at St Paul's Cathedral. Wreaths are to be laid at the September 11 Memorial Garden near the US embassy.
In the first of the global memorials, the US rugby team attended an emotional service in New Zealand, hours ahead of their opening World Cup match against Ireland.
Australian Foreign Minister Kevin Rudd and his French counterpart Alain Juppe, laid a wreath to honour those who have fought for freedom at the Australian War Memorial in Canberra.
In Japan, families gathered in Tokyo to pay their respects to the 23 Fuji Bank employees, who were killed in the attack. A dozen of the workers were Japanese.
South Korea's President Lee Myung-bak sent a letter to US President Barack Obama, conveying his "deepest condolences" to the victims of the 9/11 tragedy, their bereaved families and the American public.
Pakistan, which is under pressure to uproot terror safe havens from its soil, pledged to strengthen international cooperation to eliminate terrorism and asked the world community to uphold ideals like tolerance.
Earlier in an interview to NBC news channel, Obama said he remembered September 11, 2001 as a day when a tried and tested US "came together" in the face of disaster. 'America came together'
"For me, like for most of us, our first reaction was and continues to be just heartbreak for the families involved," Obama said.
"The other thing that we all remember is how America came together...And so 10 years later, I'd say America came through this thing in a way that was consistent with our character," the President said.
"We made mistakes. Some things haven't happened as quickly as they needed to, but overall we took the fight to al-Qaeda," he added.
Meanwhile, the Taliban have said that their movement had no role in the 9/11 attacks and accused the US of using the incident to invade Afghanistan where they have killed tens of thousands of innocent Afghans.
In a defiant statement emailed to media, the Taliban accused the US of using the September 11 attacks as a pretext to invade Afghanistan.
"Each year, 9/11 reminds the Afghans of an event in which they had no role whatsoever," the Taliban said. "American colonialism has shed the blood of tens of thousands of miserable and innocent Afghans."