Americans stood in silence to remember the nearly 3,000 people killed in the September 11 attacks on Tuesday as Osama bin Laden resurfaced to praise the suicide hijackers who carried them out six years ago to the day.

New Yorkers observed silent moments at the very times jets crashed into the World Trade Center towers and when each tower collapsed. Ceremonies took place also at the Pentagon and at a Pennsylvania field where the third and fourth planes crashed.

Defense Secretary Robert Gates vowed revenge on anyone who might attack the United States.

"The enemies of America, the enemies of our values and our liberty, will never again rest easy for we will hunt them down relentlessly and without reservation," he said in Washington outside the section of the Pentagon that was struck.

Bin Laden, the al Qaeda leader behind the attacks, defied the United States with a new audiotape. On it, he praised "the 19 champions" who hijacked the U.S. planes and crashed them.

In New York, bagpipes played, accompanied by a steady drum beat, in a park neighboring the former disaster site known as Ground Zero, which is now a busy construction zone. Church bells pealed to mark the moment.

"Six years have passed, and our place is still by your side," New York Mayor Michael Bloomberg told the gathered family and friends of those who died.

Rain fell on the somber ceremony, where many wore funereal black to remember the 2,750 killed when the towers fell. Their names were read aloud, taking hours, in what has become an annual tradition.

In all, 2,993 people died, including the 19 hijackers.

President George W. Bush, Vice President Dick Cheney and their wives led a moment of silence on the White House lawn at 8:46 a.m., when the first plane struck in New York.


About 200 Republican and Democratic lawmakers gathered, as they did on the night of the attacks, on the steps of the U.S. Capitol, and sang "God Bless America" on Monday night.

"Six years ago, Republicans and Democrats stood united on these steps, and we stand united again today," House of Representatives Republican Leader John Boehner of Ohio said.

Near Shanksville, Pennsylvania, hundreds gathered in the field where United Flight 93 crashed after passengers fought al Qaeda hijackers in the cockpit.

September 11 fell on a Tuesday for the first time since 2001, adding to the meaning of the day for many.

"There's a lot of symbolism about what happened, and the whole country is drawn into it," Elizabeth Boyer, whose cousin Edward Calderon was killed, said at the World Trade Center. "This is the place. We don't have a cemetery to go to."

Last week bin Laden urged Americans to convert to Islam in his first new video for nearly three years, following al Qaeda's pattern of issuing statements to mark September 11.

"Certainly the capture of bin Laden would be of enormous symbolic importance, but the fact is that the war against terror is not a war against one guy," White House spokesman Tony Snow said.

The attacks jolted Bush's presidency and led to the U.S. invasion of Afghanistan to root out al Qaeda plotters protected there by the former Taliban government, though bin Laden is believed to have escaped.

Bush also invaded Iraq, although many critics say the unpopular conflict has drained resources from the global war on terrorism he declared after September 11.

"We've killed God-knows-how-many Iraqis. We probably couldn't name one of them, and they had nothing to do with 9/11," said Meyer Settler, 67, a bookkeeper on his way to work near the World Trade Center site, as the names of September 11 victims were being read out one after another.

(Additional reporting by Daniel Trotta in New York and David Morgan, Thomas Ferraro and Tabassum Zakaria in Washington)