9/11 Anniversary: Obama Leads US In Mourning

US President Barack Obama and former President George Bush have joined hundreds of families at Ground Zero in New York for a service marking the 10th anniversary of the 9/11 attacks.

Nearly 3,000 people died when al Qaeda hijackers brought down the World Trade Centre towers, flew a plane into the Pentagon and into a field in Pennsylvania.

As happens every year, the names of all those who perished were read out at the memorial event in lower Manhattan where the Twin Towers once stood.

Their names are also inscribed in bronze on the perimeter of the two huge pools in the shape of the buildings that collapsed on the morning of September 11, 2001.

Before the service President Obama visited the North Memorial Pool, which sits in the footprint of the north tower.

He walked around the pool hand-in-hand with his wife Michelle, accompanied by Mr Bush and his wife Laura.

In a sombre moment, Mr Obama touched the names of the dead before greeting some family members and dignitaries.

The remembrance ceremony began at 8.40am local time with pipers and drummers leading a procession with the World Trade Centre flag to the stage.

It was followed by the first of six pauses at 8.46am.

Two of the pauses are to mark the times that each plane hit the towers and two are to mark the time when each tower fell.

The others mark the times of the attacks on the Pentagon and on Flight 93 in Shanksville.

After the first pause Mr Obama and New York Mayor Mike Bloomberg gave readings.

Relatives of those who died in the World Trade Centre attacks then read out their names.

Mr Bush, who was president at the time of 9/11, gave a reading after the second moment of silence.

Law enforcement authorities in New York and Washington were on high alert after what was described as a "credible but unconfirmed" threat of an attack by al Qaeda.

Security was especially tight in Manhattan, where police set up vehicle checks on streets and at bridges and tunnels leading into the city.

Barricades were placed on every block near Ground Zero, with police asking members of the public for identification.

Thousands of people gathered near the site, some clutching American flags, to watch a large screen set up to show the remembrance ceremony.

Some wore T-shirts reading, "Never Forget," a slogan popular since the attacks.

Mr Obama and his wife Michelle will later travel to Shanksville in Pennsylvania, where airline passengers fought back against hijackers and drove a plane into the ground.

It was believed the hijackers intended to fly the jet into the White House or the Capitol building.

The president will then return to Washington to lay a wreath at the Pentagon and attend the "Concert for Hope" at the Kennedy Centre.

In a message earlier, Mr Obama said: "A decade ago, our fellow citizens and first responders rushed up stairwells, into flames, and into that cockpit and gave their lives to save others.

"In the decade since, a new generation - our military personnel, intelligence officers, and law enforcement - has stepped forward to serve our country and keep us safe.

"This weekend, I encourage all Americans to remember not only the innocent lives we lost on that day, but to remember the ordinary goodness and patriotism of the American people and the spirit of unity that brought us together during the days and weeks after the attacks of September 11."