by Giles Hewitt
NEW YORK, Sept 11 (AFP) - The United States Saturday recalled the horror of the September 11 attacks with tears and defiance, in sombre ceremonies shadowed by fresh terrorist threats, fighting in Iraq and a divisive presidential election campaign.
In a live radio address from the Oval Office, where he was joined by victims' relatives, President George W. Bush used the third anniversary of the attacks to pledge an unrelenting hunt for terrorists around the world.
"The United States is determined to stay on the offensive and to pursue the terrorists wherever they train or sleep or attempt to set down roots," Bush said.
"We know that there is still a danger to America, so we will not relent until the terrorists who plot murder against our people are found and dealt with," he added.
Earlier, on the lawn of the White House, Bush led the nation in a minute of silence that began at 8:46 am (1246 GMT) -- the time when the first of four airliners hijacked by Al-Qaeda members slammed into New York's World Trade Center.
At Ground Zero, the focus of the day's remembrance events, parents and grandparents, their voices choked with emotion, read out the names of the 2,749 people who died in the attacks on the twin trade center towers.
"There is no name for a parent who loses a child, for there are no words to describe this pain," New York Mayor Michael Bloomberg said at the start of the sombre ceremony.
The third anniversary carried particular resonance for the victims' families, as it marked perhaps the last time they would be able to descend into the pit of Ground Zero, given the reconstruction plans for the site.
Many carried roses down to the bedrock and placed them in two square pools of water -- a scaled-down version of what will become part of a permanent memorial to those who died.
Others held up portraits of their lost loved ones, with messages that ranged from expressions or remembrance and grief to those of anger and revenge.
"Still waiting for justice" read one placard.
Hatred of the perpetrators of the attacks has been mixed with the resentment of some families towards the US authorities, whom they charge with failing to provide a full accounting of the circumstances leading up to September 11.
The reading of the names paused four times during the ceremony, twice to mark the impact of the two planes, and twice more for the times each tower fell.
Later in the evening, two powerful spotlights will send two shafts of light up into the night sky to symbolise the fallen structures.
Ceremonies were also held at the Pentagon for the 184 people who died in the attack there, and in the field in Pennsylvania where the fourth airliner, carrying 44 people, crashed after passengers staged a rebellion against the hijackers.
Another taunting reminder of the traumatic events of three years ago came Thursday in the form of a video statement by Al-Qaeda number-two Ayman al-Zawahiri.
Osama bin Laden's deputy said defeat for US forces in Iraq and Afghanistan was just a matter of time and warned that Americans would not be safe while their government "commits crimes against Muslims in Iraq and Afghanistan and Palestine."
The US State Department Friday urged US citizens abroad to be vigilant, warning that Al-Qaeda and affiliated groups were preparing to strike US interests overseas.
For Bush, September 11 remains the defining moment of his presidency and the foundation of his national security policy, which he has placed at the centre of his campaign for re-election in November.
The human cost of the open-ended war on terror launched by Bush in the wake of the attacks was underlined just days before the third anniversary, when the death toll among US soldiers in Iraq crossed the 1,000 mark.
Bush's Democratic challenger, Senator John Kerry, who has accused the president of using the war on terror as a political tool to scare the American people, attended a commemorative event in his hometown of Boston on Saturday.
"While September 11 was the worst day we have ever seen, it brought out the best in all of us," Kerry said at the ceremony at Boston's opera house.
"We will always remember where we were on that day. And we must always remember that we will only defeat those who sought to destroy us by standing together as one America," he declared.
Some of the hijacked planes used in the September 11 attacks took off from Boston.
Despite the somber atmosphere in New York, there were also clear signs that the city and its inhabitants are increasingly looking to the future.
The gaping scar that was Ground Zero is already a burgeoning construction site, where a groundbreaking ceremony was held July 4, Independence Day, for the symbolic 1,776-foot (540-meter) Freedom Tower that will form the centrepiece of the redeveloped site.
The city's economy is back on track after three harsh years, with tourist numbers back up and small businesses returning in force to the lower Manhattan area.
A deadline yesterday for lawsuits related to the September 11 attacks prompted a rush to a New York federal courthouse.
The Port Authority of New York and New Jersey, the owner of the World Trade Center, filed a suit for damages against Saudi Arabia, alleging that the Saudi royal family had helped support Al-Qaeda for years.