Americans around the world are marking the 11th anniversary of terrorist attacks on New York, Washington and Pennsylvania to honor more than 3,000 people who lost their lives in the attacks.

U.S. President Barack Obama said Tuesday that the September 11 victims would be remembered “no matter how many years pass.”

Mr. Obama addressed an audience under clear blue skies outside the Pentagon where 184 of the victims were killed on an equally sunny day when a suicide attacker drove a plane into the building. He reiterated that Americans are not fighting Islam, but the al-Qaida terrorists and their allies.

In New York, the commemoration began with reading the names of the victims of all three attacks at the site where two twin towers once stood.

Moments of silence were held across the United States and in the U.S. embassies around the world.

President Obama and his wife Michelle observed a moment of silence at the White House lawn before heading to the Pentagon.

Vice President Joe Biden addressed a commemoration in Shanksville, Pennsylvania, where 40 passengers were killed in a fourth plane that crashed as the passengers fought the hijackers.

U.S. authorities say the hijackers planned to crash that plane into the U.S. Capitol in Washington.

After the ceremony at the Pentagon, President Obama and first lady Michelle stopped at Arlington National Cemetery to visit the graves of service members killed in Afghanistan and Iraq.

U.S. Defense Secretary Leon Panetta on Monday visited the memorial in Shanksville dedicated to the victims. He said the country must never forget the military personnel deployed to Afghanistan in 2001 to battle Taliban forces who gave shelter to al Qaida and its leader, Osama bin Laden after the terrorist attacks he ordered.

Republican presidential candidate Mitt Romney marked the September 11 anniversary in an address to the National Guard Association in Reno, in (the western U.S. state of) Nevada.