WASHINGTON - Americans from the nation's capital to Alaska marked Memorial Day with parades, somber reflection and even a climbing expedition in a holiday infused with fresh meaning by the approaching 10th anniversary of the Sept. 11 terrorist attacks.

A soldier helps US President Barack Obama (2nd L) lay a Memorial Day wreath at the Tomb of the Unknowns at Arlington Cemetery in Arlington, Virginia, May 30, 2011. [Photo/Agencies]

The National Memorial Day Parade in Washington honored veterans and America's war dead but also featured special tributes to Sept 11 first responders, victims and their families. Also fresh in the minds of parade participants and watchers was the killing less than a month ago of Osama bin Laden, who masterminded the attacks.

Elsewhere, military jets thundered through the sky above New York after a wreath-laying ceremony aboard an aircraft carrier that's been turned into a museum, while hundreds of volunteers put small flags on the 25,000 graves at a sprawling military cemetery near Las Vegas. US troops fighting in Afghanistan also took time out to remember fallen comrades.

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Along the parade route in Washington, children sat on parents' shoulders and throngs cheered the passing high school marching bands and floats of war veterans. Special guests included Medal of Honor recipients, astronaut and Korean War veteran Buzz Aldrin and actor Gary Sinise, a veterans advocate who played Lt. Dan in the Oscar-winning film "Forrest Gump."

Hamilton Peterson, who lost his father and stepmother when the hijacked United Airlines 93 crashed into a field in Shanksville, Pa., said the looming anniversary of the terror attacks should serve as a reminder to Americans to be vigilant.

"Obviously, bin Laden's death is a highlight of the 10th anniversary. However, we recognize that future attacks are imminent and that, absent using 9/11 as a model for how to respond, all Americans need to get involved. It can't just be the military," said Peterson, 51.

Sgt. James Patrick McMichael of the Arlington County, Va., sheriff's office was among the first responders to the Pentagon and was diagnosed with post-traumatic stress disorder about two years later. He said that even though the anniversary was dredging up painful memories, it's still critical that the public never lose memory of the attacks — especially to make sure they don't happen again.

A commercial jet crashed into the Pentagon on Sept 11, killing 184 people at the sprawling Defense Department headquarters.

"Reliving the event is not something that I look forward to, but I don't think it should be something that's not brought up to the public," said McMichael, who attended the parade in Washington. "I don't think people should forget about what occurred."

The parade featured a Shanksville fire engine and a red, white and blue float bearing the images of the victims on miniature twin towers.

Seventeen-year-old spectator Zach Garrett recalled watching coverage of the attacks as a third-grader.

"Watching it on the TV, it was disturbing at that age," said the Alpharetta, Ga., resident who was visiting Washington with his family. "And here, 10 years later, this big parade — everybody's participating and everybody's on the sidelines cheering everybody on. There's a lot of patriotism here."

President Barack Obama participated in a wreath-laying ceremony at the Tomb of the Unknowns at Arlington National Cemetery near Washington.

"Our nation owes a debt to its fallen heroes that we cannot ever fully repay," Obama said in a speech. "But we can honor their sacrifice, and we must."

In New York, Lynn Berat dressed her young daughters in matching red, white and blue sundresses for a the ceremony at the Intrepid Sea, Air & Space Museum on the west side of Manhattan.

"I think it's important that they understand the spirit of Memorial Day instead of just barbecuing," she said.

Five Army Rangers stationed at Joint Base Lewis-McChord in Washington state climbed Mount McKinley in Alaska, reaching the summit Friday night in honor of 11 Rangers from their regiment who have died in the line of duty. They planted a flag at the summit bearing the names of the fallen.

At the cemetery near Las Vegas, 87-year-old World War II veteran Bernard Miller was among hundreds who placed the small flags on graves.

"A lot of my friends are buried here," Miller said afterward, standing in a bright red jacket and cap with insignia marking his Marine service. "They've done their job. I could be there with them, but the good Lord doesn't want me right now."

US troops fighting in Afghanistan paused for Memorial Day services, with some praying and holding flag-raising ceremonies to recognize the more than 1,400 who have been killed in combat there since the war began a decade ago.

Obama plans to draw down US troops in Afghanistan beginning in July, while NATO has committed to handing over control of security in the country to Afghans by 2014. For now, though, the war continues.

"We reflect on those who have gone before us. We reflect on their service and their sacrifice on behalf of our great nation," said Brig. Gen. Lewis A. Craparotta, who commands a Marine division in Afghanistan's southern Helmand province. "We should also remember those serving today who embody that same commitment of service and sacrifice."