ARLINGTON, VA - President Barack Obama is leading the nation in remembering its war heroes, the fallen and those still defending the flag in a Memorial Day tribute.

The president, just back from a surprise visit with troops in Afghanistan, placed a wreath at Arlington National Cemetery.

With troops in formal military dress standing at attention, Obama walked to the site of the Tomb of the Unknowns.

The president has directed all government agencies in the United States to fly their flags at half-staff in observance of Memorial Day.