The United States Tuesday is marking the sixth anniversary of the September 11, 2001 terrorist attacks with somber ceremonies.

President Bush and first lady Laura Bush, are joined by Vice President Dick Cheney and his wife, Lynne Cheney, as they take part in a moment of silence, marking the sixth anniversary of the terrorist attacks, 11  Sep 2007

President Bush paused for a moment of silence at the White House at 8:46 am EDT to mark the time six years ago when the first hijacked airplane hit the World Trade Center in New York City.

In New York, rescue workers and families of the victims are reading out the names of the more than 2,750 people killed after two hijacked planes crashed into the World Trade Center towers and the two 110-story buildings collapsed.

Defense Secretary Robert Gates spoke at a ceremony at the Pentagon, where 184 people died after hijackers crashed a plane into the building six years ago. In Pennsylvania, mourners are remembering the 40 people who died after passengers overtook hijackers and the plane went down in a field.

The key planner of the attacks, al-Qaida leader Osama bin Laden, has released a videotape eulogizing one of the 19 suicide hijackers.

Bin Laden is shown in a still image on the video urging sympathizers to join what he called the "caravan" of martyrs as he praises hijacker Walid al-Shehri, who took part in the World Trade Center attack.

After bin Laden speaks, there is a video of al-Shehri condemning the United States.

The new message comes days after bin Laden appeared in his first video in nearly three years. In it, he urges Americans to abandon their democratic system of government and embrace Islam.

Bin Laden and his deputy, Ayman al-Zawahiri, are believed to be hiding in the border area between Afghanistan and Pakistan.