U.S. President Barack Obama has marked the eighth anniversary of theSeptember 11, 2001 attacks on the United States by reaffirming hisdetermination to defeat terrorism. The president laid a wreath inmemory of those who died on that day's attack on the Pentagon.

President Obama stood in a heavy rain at the Pentagon Memorial, and called on Americans to remain united in fighting terrorism.

Obama Marks September 11 Anniversary In Washington

"Letus renew our resolve against those who perpetrated this barbaric actand who plot against us still," the president said. "In defense of ournation, we will never waver. In pursuit of al-Qaida and its extremistallies, we will never falter."

Obama Marks September 11 Anniversary In Washington

Near the spot where, eight yearsearlier, a hijacked jetliner slammed into the huge office building,killing 184 people, Mr. Obama pledged to do everything possible to keepAmerica safe. And he said recalling the nation's unity of purposeafter the 9/11 attacks is the strongest rebuke against the terroristswho conducted them.

Obama Marks September 11 Anniversary In Washington

"On a day when others sought to sap ourconfidence, let us renew our common purpose," President Obama said."Let us remember how we came together as one nation, as one people, asAmericans."

The president addressed about 500 people, includingsurvivors of the Pentagon attack and families of the victims. He saidthat despite the brutality of the attacks, Americans should recall thebeauty of the victims' lives.

"They were innocent. Harming noone, they went about their daily lives," the president said. "Gone ina terrible instant, they now dwell in the house of the Lord forever."

Mr.Obama also paid tribute to the public safety workers who responded tothe Pentagon attack, as well as the military personnel who have foughtto protect the nation since 9/11.

The president and Defense Secretary Robert Gates met with the victims' family members.

Thefirst of four moments of silence was held at 8:46 a.m., the time thefirst jet hit the twin towers of New York's World Trade Center eightyears earlier. At that time, the president and first lady MichelleObama observed a moment of silence outside the White House as a buglerplayed taps. About 150 White House staff members stood in silencearound them.

In New York, families carrying photos of lost lovedones gathered where the World Trade Center had once stood, and huddledin the rain as church bells rang in remembrance. Vice President JoeBiden laid flowers in a reflecting pool at the site. The names of thevictims were being read throughout the day.

Most of the nearly 3,000 people who died in the 9-11 attacks were in or near the towers.

FormerSecretary of State Colin Powell was to give the main speech at theceremonies near Shanksville, Pennsylvania, where a fourth hijackedplane crashed. The names of the 40 passengers and crew of that flightwere to be read. It is widely believed that passengers on UnitedAirlines Flight 93 foiled a hijackers' plot to ram the plane into amajor landmark in Washington.