The United States marks the fifth anniversary of the September 11 attacks today with solemn ceremonies and silent tributes to the nearly 3,000 people who died, but still haunted by Al-Qaida and the war in Iraq.

President George W. Bush, who was less than eight months into his first term when Al-Qaida hijackers took over four passenger jets and flew them into New York's World Trade Center, the Pentagon and a Pennsylvania field, will lead the commemorations.

At the start of two days of ceremonies, Bush was set yesterday to lay a wreath at Ground Zero, the gaping hole where the Twin Towers once stood and the enduring symbol of the biggest attack on US soil since Pearl Harbor 60 years before.

Bush has called for flags to fly at half mast and for people across the country to observe a moment of silence at 8:46 am (1246 GMT) today, the exact time that the first of two planes ploughed into the World Trade Center.

He is then to lay a wreath in the Pennsylvania field where a third jet crashed after passengers fought back against their hijackers and where 40 people were killed.

He will then fly to the Pentagon for commemorations there.

In what has become an annual ritual, husbands, wives and partners of the 2,749 people who perished in the World Trade Center will read a roll call of the dead, pausing only to mark the moments the planes struck and the towers collapsed.

As evening falls, two giant beams of light symbolising the collapsed towers will illuminate the Manhattan sky. A candlelight vigil is then planned at Ground Zero.

For only the fifth time in his presidency, Bush will deliver a televised address to the nation from the White House in the evening, in what has been billed as "a non-political speech about what September 11 has meant to the nation."

In the run-up to the anniversary, Bush has made several speeches justifying decisions made in the name of the so-called "war on terror."

"America still faces determined enemies," Bush said in the latest on Saturday. "We must take the words of these extremists seriously, and we must act decisively to stop them from achieving their evil aims."

Five years after the attacks left the world's superpower reeling, September 11 remains the defining moment of Bush's presidency and a watershed in recent American history, its shockwaves continuing to reverberate.

The attacks spurred America to go to war in Afghanistan and Iraq, polarising public opinion, reshaping the diplomatic landscape and straining old alliances.

Bin Laden at large

Five years on, Al-Qaida leader Osama bin Laden remains at large, despite extensive efforts to track him down in his suspected hideouts in the mountainous tribal belt straddling the border between Afghanistan and Pakistan.

Years of hunting in the barren mountains that divide the two Islamic republics have wiped out many of his former henchmen but thrown up no hint of the Saudi-born kingpin, while new recruits continue to emerge.

As in previous years, Arab television broadcast fresh Al-Qaida video footage just days ahead of the anniversary this time purportedly showing bin Laden and two of the 19 hijackers preparing for the attacks.

Since September 11, the Islamist militant group has launched attacks on both London and Madrid, killing hundreds of people in reprisal for Britain and Spain's support of the US-led invasion of Iraq in March 2003.

Source: China Daily