"As we remember the victims, their families, and the heroes who stood up during one of our country's darkest moments, I invite all Americans to reclaim that abiding spirit of compassion by serving their communities in the days and weeks ahead," Obama said in a proclamation released Monday by the White House.
In December 2001, Congress designated Sept. 11 as Patriot Day. In April 2009, Congress requested the observance of Sept. 11 as an annually recognized National Day of Service and Remembrance.
"More than a decade later, the world we live in is forever changed," the proclamation read. "But as we mark the anniversary of Sept. 11, we remember what remains the same: our character as a nation, our faith in one another, and our legacy as a country strengthened by service and selflessness."
In the proclamation, Obama called on federal departments and agencies to fly the flag at half staff in memory of those who died Sept. 11, 2001, when two planes struck the World Trade Center in New York and the Pentagon in Washington. A fourth plane crashed in a field in Pennsylvania as passengers stormed the cockpit.