WASHINGTON, Sept. 11 (UPI) -- Rain and overcast skies reflected the somber mood in New York Friday as thousands gathered to remember victims of the terrorist attacks eight years ago.

The American flag recovered from the attack was presented before New York Mayor Michael Bloomberg opened the remembrance near where the World Trade Center's Twin Towers once stood.

President Barack Obama declared Sept. 11 a national day of remembrance and service.

"We will safeguard the memories of those who died by rekindling (their) spirit of service," Bloomberg said.

A bell rang twice during the ceremony, starting moments of silence at 8:46 a.m. EDT when the North Tower was struck by American Airlines Flight 11, and at 9:03 a.m. EDT when United Airlines Flight 175 rammed the South Tower.

Friends and families tossed flowers into a fountain in memory of loved ones who died. New York Gov. David Paterson and Vice President Joe Biden read poetry, family members offered memories and police officers stood at attention in the wind-whipped rain.

A mournful strain of a cello provided background music as a family members read the names of the 2,751 people who died when the towers collapsed.

At the White House, President Barack Obama and first lady Michelle Obama stood in a drizzle to observe a moment of silence. A bell rang three times then they bowed their heads for a minute, placing their hands over their hearts as a bugler played "Taps."

Obama was to go to the Pentagon to make remarks and participate in a wreath-laying ceremony for the 184 victims who died when American Airlines Flight 77 struck the building.

In Shankesville, Pa., near where United Airlines Flight 93 went down after passengers revolted against the hijackers, an American flag indicated the point where the plane crashed into the clearing. Former U.S. Secretary of State Colin Powell was to deliver the keynote address.